Release MobileDet code and model, and require tf_slim installation for OD API. (#8562)

* Merged commit includes the following changes:
311933687  by Sergio Guadarrama:

    Removes spurios use of tf.compat.v2, which results in spurious tf.compat.v1.compat.v2. Adds basic test to nasnet_utils.
    Replaces all remaining import tensorflow as tf with import tensorflow.compat.v1 as tf

--
311766063  by Sergio Guadarrama:

    Removes explicit tf.compat.v1 in all call sites (we already import tf.compat.v1, so this code was  doing tf.compat.v1.compat.v1). The existing code worked in latest version of tensorflow, 2.2, (and 1.15) but not in 1.14 or in 2.0.0a, this CL fixes it.

--
311624958  by Sergio Guadarrama:

    Updates README that doesn't render properly in github documentation

--
310980959  by Sergio Guadarrama:

    Moves research_models/slim off tf.contrib.slim/layers/framework to tf_slim

--
310263156  by Sergio Guadarrama:

    Adds model breakdown for MobilenetV3

--
308640...

research/object_detection/models/ssd_mobilenet_v2_keras_feature_extractor.py

@@ -16,7 +16,7 @@
 
 """SSDFeatureExtractor for MobilenetV2 features."""
 
-import tensorflow as tf
+import tensorflow.compat.v1 as tf
 
 from object_detection.meta_architectures import ssd_meta_arch
 from object_detection.models import feature_map_generators

research/object_detection/models/ssd_mobilenet_v2_mnasfpn_feature_extractor.py

@@ -22,16 +22,15 @@ from __future__ import print_function
 import collections
 import functools
 from six.moves import range
-import tensorflow as tf
+import tensorflow.compat.v1 as tf
 
-from tensorflow.contrib import slim as contrib_slim
+import tf_slim as slim
 from object_detection.meta_architectures import ssd_meta_arch
 from object_detection.utils import ops
 from object_detection.utils import shape_utils
 from nets.mobilenet import mobilenet
 from nets.mobilenet import mobilenet_v2
 
-slim = contrib_slim
 
 Block = collections.namedtuple(
     'Block', ['inputs', 'output_level', 'kernel_size', 'expansion_size'])

research/object_detection/models/ssd_mobilenet_v2_mnasfpn_feature_extractor_test.py

@@ -15,14 +15,11 @@
 # ==============================================================================
 """Tests for ssd_mobilenet_v2_nas_fpn_feature_extractor."""
 import numpy as np
-import tensorflow as tf
+import tensorflow.compat.v1 as tf
 
-from tensorflow.contrib import slim as contrib_slim
 from object_detection.models import ssd_feature_extractor_test
 from object_detection.models import ssd_mobilenet_v2_mnasfpn_feature_extractor as mnasfpn_feature_extractor
 
-slim = contrib_slim
-
 
 class SsdMobilenetV2MnasFPNFeatureExtractorTest(
     ssd_feature_extractor_test.SsdFeatureExtractorTestBase):

research/object_detection/models/ssd_mobilenet_v3_feature_extractor.py

@@ -14,8 +14,8 @@
 # ==============================================================================
 """SSDFeatureExtractor for MobileNetV3 features."""
 
-import tensorflow as tf
-from tensorflow.contrib import slim as contrib_slim
+import tensorflow.compat.v1 as tf
+import tf_slim as slim
 
 from object_detection.meta_architectures import ssd_meta_arch
 from object_detection.models import feature_map_generators
@@ -25,8 +25,6 @@ from object_detection.utils import shape_utils
 from nets.mobilenet import mobilenet
 from nets.mobilenet import mobilenet_v3
 
-slim = contrib_slim
-
 
 class SSDMobileNetV3FeatureExtractorBase(ssd_meta_arch.SSDFeatureExtractor):
   """Base class of SSD feature extractor using MobilenetV3 features."""

research/object_detection/models/ssd_mobilenet_v3_feature_extractor_test.py

@@ -14,14 +14,14 @@
 # ==============================================================================
 """Tests for ssd_mobilenet_v3_feature_extractor."""
 
-import tensorflow as tf
-from tensorflow.contrib import slim as contrib_slim
+import tensorflow.compat.v1 as tf
+import tf_slim as slim
 
 from object_detection.models import ssd_mobilenet_v3_feature_extractor
 from object_detection.models import ssd_mobilenet_v3_feature_extractor_testbase
 
 
-slim = contrib_slim
+slim = slim
 
 
 class SsdMobilenetV3LargeFeatureExtractorTest(

research/object_detection/models/ssd_mobilenet_v3_feature_extractor_testbase.py

@@ -17,15 +17,11 @@
 import abc
 
 import numpy as np
-import tensorflow as tf
-from tensorflow.contrib import slim as contrib_slim
+import tensorflow.compat.v1 as tf
 
 from object_detection.models import ssd_feature_extractor_test
 
 
-slim = contrib_slim
-
-
 class _SsdMobilenetV3FeatureExtractorTestBase(
     ssd_feature_extractor_test.SsdFeatureExtractorTestBase):
   """Base class for MobilenetV3 tests."""

research/object_detection/models/ssd_pnasnet_feature_extractor.py

@@ -19,8 +19,8 @@
 Based on PNASNet ImageNet model: https://arxiv.org/abs/1712.00559
 """
 
-import tensorflow as tf
-from tensorflow.contrib import slim as contrib_slim
+import tensorflow.compat.v1 as tf
+import tf_slim as slim
 
 from object_detection.meta_architectures import ssd_meta_arch
 from object_detection.models import feature_map_generators
@@ -29,8 +29,6 @@ from object_detection.utils import ops
 from object_detection.utils import variables_helper
 from nets.nasnet import pnasnet
 
-slim = contrib_slim
-
 
 def pnasnet_large_arg_scope_for_detection(is_batch_norm_training=False):
   """Defines the default arg scope for the PNASNet Large for object detection.

research/object_detection/models/ssd_pnasnet_feature_extractor_test.py

@@ -15,14 +15,11 @@
 
 """Tests for ssd_pnas_feature_extractor."""
 import numpy as np
-import tensorflow as tf
-from tensorflow.contrib import slim as contrib_slim
+import tensorflow.compat.v1 as tf
 
 from object_detection.models import ssd_feature_extractor_test
 from object_detection.models import ssd_pnasnet_feature_extractor
 
-slim = contrib_slim
-
 
 class SsdPnasNetFeatureExtractorTest(
     ssd_feature_extractor_test.SsdFeatureExtractorTestBase):

research/object_detection/models/ssd_resnet_v1_fpn_feature_extractor.py

@@ -23,8 +23,8 @@ from __future__ import division
 from __future__ import print_function
 
 from six.moves import range
-import tensorflow as tf
-from tensorflow.contrib import slim as contrib_slim
+import tensorflow.compat.v1 as tf
+import tf_slim as slim
 
 from object_detection.meta_architectures import ssd_meta_arch
 from object_detection.models import feature_map_generators
@@ -33,8 +33,6 @@ from object_detection.utils import ops
 from object_detection.utils import shape_utils
 from nets import resnet_v1
 
-slim = contrib_slim
-
 
 class SSDResnetV1FpnFeatureExtractor(ssd_meta_arch.SSDFeatureExtractor):
   """SSD FPN feature extractor based on Resnet v1 architecture."""

research/object_detection/models/ssd_resnet_v1_fpn_feature_extractor_test.py

@@ -13,7 +13,7 @@
 # limitations under the License.
 # ==============================================================================
 """Tests for ssd resnet v1 FPN feature extractors."""
-import tensorflow as tf
+import tensorflow.compat.v1 as tf
 
 from object_detection.models import ssd_resnet_v1_fpn_feature_extractor
 from object_detection.models import ssd_resnet_v1_fpn_feature_extractor_testbase

research/object_detection/models/ssd_resnet_v1_fpn_feature_extractor_testbase.py

@@ -22,7 +22,7 @@ import abc
 from absl.testing import parameterized
 import numpy as np
 from six.moves import zip
-import tensorflow as tf
+import tensorflow.compat.v1 as tf
 
 from object_detection.models import ssd_feature_extractor_test
 

research/object_detection/models/ssd_resnet_v1_fpn_keras_feature_extractor.py

@@ -22,7 +22,7 @@ from __future__ import print_function
 
 from six.moves import range
 from six.moves import zip
-import tensorflow as tf
+import tensorflow.compat.v1 as tf
 
 from object_detection.meta_architectures import ssd_meta_arch
 from object_detection.models import feature_map_generators

research/object_detection/models/ssd_resnet_v1_ppn_feature_extractor.py

@@ -15,8 +15,8 @@
 # ==============================================================================
 """SSD feature extractors based on Resnet v1 and PPN architectures."""
 
-import tensorflow as tf
-from tensorflow.contrib import slim as contrib_slim
+import tensorflow.compat.v1 as tf
+import tf_slim as slim
 
 from object_detection.meta_architectures import ssd_meta_arch
 from object_detection.models import feature_map_generators
@@ -25,8 +25,6 @@ from object_detection.utils import ops
 from object_detection.utils import shape_utils
 from nets import resnet_v1
 
-slim = contrib_slim
-
 
 class _SSDResnetPpnFeatureExtractor(ssd_meta_arch.SSDFeatureExtractor):
   """SSD feature extractor based on resnet architecture and PPN."""

research/object_detection/models/ssd_resnet_v1_ppn_feature_extractor_test.py

@@ -13,7 +13,7 @@
 # limitations under the License.
 # ==============================================================================
 """Tests for ssd resnet v1 feature extractors."""
-import tensorflow as tf
+import tensorflow.compat.v1 as tf
 
 from object_detection.models import ssd_resnet_v1_ppn_feature_extractor
 from object_detection.models import ssd_resnet_v1_ppn_feature_extractor_testbase

research/object_detection/models/ssd_resnet_v1_ppn_feature_extractor_testbase.py

@@ -15,7 +15,7 @@
 """Tests for ssd resnet v1 feature extractors."""
 import abc
 import numpy as np
-import tensorflow as tf
+import tensorflow.compat.v1 as tf
 
 from object_detection.models import ssd_feature_extractor_test
 

research/object_detection/predictors/convolutional_box_predictor.py

@@ -21,14 +21,12 @@ from __future__ import print_function
 import functools
 from six.moves import range
 from six.moves import zip
-import tensorflow as tf
-from tensorflow.contrib import slim as contrib_slim
+import tensorflow.compat.v1 as tf
+import tf_slim as slim
 from object_detection.core import box_predictor
 from object_detection.utils import shape_utils
 from object_detection.utils import static_shape
 
-slim = contrib_slim
-
 BOX_ENCODINGS = box_predictor.BOX_ENCODINGS
 CLASS_PREDICTIONS_WITH_BACKGROUND = (
     box_predictor.CLASS_PREDICTIONS_WITH_BACKGROUND)

research/object_detection/predictors/convolutional_box_predictor_test.py

@@ -24,7 +24,7 @@ from absl.testing import parameterized
 import numpy as np
 from six.moves import range
 from six.moves import zip
-import tensorflow as tf
+import tensorflow.compat.v1 as tf
 
 from google.protobuf import text_format
 from object_detection.builders import box_predictor_builder

research/object_detection/predictors/convolutional_keras_box_predictor.py

@@ -22,7 +22,7 @@ from __future__ import print_function
 import collections
 
 from six.moves import range
-import tensorflow as tf
+import tensorflow.compat.v1 as tf
 
 from object_detection.core import box_predictor
 from object_detection.utils import shape_utils

research/object_detection/predictors/convolutional_keras_box_predictor_test.py

@@ -15,7 +15,7 @@
 
 """Tests for object_detection.predictors.convolutional_keras_box_predictor."""
 import numpy as np
-import tensorflow as tf
+import tensorflow.compat.v1 as tf
 
 from google.protobuf import text_format
 from object_detection.builders import box_predictor_builder

research/object_detection/predictors/heads/box_head.py

@@ -20,13 +20,11 @@ All the box prediction heads have a predict function that receives the
 `features` as the first argument and returns `box_encodings`.
 """
 import functools
-import tensorflow as tf
-from tensorflow.contrib import slim as contrib_slim
+import tensorflow.compat.v1 as tf
+import tf_slim as slim
 
 from object_detection.predictors.heads import head
 
-slim = contrib_slim
-
 
 class MaskRCNNBoxHead(head.Head):
   """Box prediction head.