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/core/balanced_positive_negative_sampler.py

@@ -30,7 +30,7 @@ It also ensures the length of output of the subsample is always batch_size, even
 when number of examples set to True in indicator is less than batch_size.
 """
 
-import tensorflow as tf
+import tensorflow.compat.v1 as tf
 
 from object_detection.core import minibatch_sampler
 

research/object_detection/core/balanced_positive_negative_sampler_test.py

@@ -16,7 +16,7 @@
 """Tests for object_detection.core.balanced_positive_negative_sampler."""
 
 import numpy as np
-import tensorflow as tf
+import tensorflow.compat.v1 as tf
 
 from object_detection.core import balanced_positive_negative_sampler
 from object_detection.utils import test_case

research/object_detection/core/batch_multiclass_nms_test.py

@@ -19,7 +19,7 @@ from __future__ import print_function
 from absl.testing import parameterized
 import numpy as np
 from six.moves import range
-import tensorflow as tf
+import tensorflow.compat.v1 as tf
 from object_detection.core import post_processing
 from object_detection.utils import test_case
 

research/object_detection/core/batcher.py

@@ -21,7 +21,7 @@ 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 prefetcher
 from object_detection.utils import tf_version

research/object_detection/core/batcher_tf1_test.py

@@ -21,13 +21,11 @@ from __future__ import print_function
 
 import numpy as np
 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.core import batcher
 
-slim = contrib_slim
-
 
 class BatcherTest(tf.test.TestCase):
 

research/object_detection/core/box_coder.py

@@ -35,7 +35,7 @@ from abc import abstractmethod
 from abc import abstractproperty
 
 import six
-import tensorflow as tf
+import tensorflow.compat.v1 as tf
 
 from object_detection.utils import shape_utils
 

research/object_detection/core/box_coder_test.py

@@ -14,7 +14,7 @@
 # ==============================================================================
 
 """Tests for object_detection.core.box_coder."""
-import tensorflow as tf
+import tensorflow.compat.v1 as tf
 
 from object_detection.core import box_coder
 from object_detection.core import box_list

research/object_detection/core/box_list.py

@@ -34,7 +34,7 @@ Some other notes:
   * Tensors are always provided as (flat) [N, 4] tensors.
 """
 
-import tensorflow as tf
+import tensorflow.compat.v1 as tf
 
 from object_detection.utils import shape_utils
 

research/object_detection/core/box_list_ops.py

@@ -28,7 +28,7 @@ from __future__ import division
 from __future__ import print_function
 
 from six.moves import range
-import tensorflow as tf
+import tensorflow.compat.v1 as tf
 
 from object_detection.core import box_list
 from object_detection.utils import ops

research/object_detection/core/box_list_ops_test.py

@@ -15,7 +15,7 @@
 
 """Tests for object_detection.core.box_list_ops."""
 import numpy as np
-import tensorflow as tf
+import tensorflow.compat.v1 as tf
 
 from object_detection.core import box_list
 from object_detection.core import box_list_ops

research/object_detection/core/box_list_test.py

@@ -15,7 +15,7 @@
 
 """Tests for object_detection.core.box_list."""
 import numpy as np
-import tensorflow as tf
+import tensorflow.compat.v1 as tf
 
 from object_detection.core import box_list
 from object_detection.utils import test_case

research/object_detection/core/box_predictor.py

@@ -27,7 +27,7 @@ These modules are separated from the main model since the same
 few box predictor architectures are shared across many models.
 """
 from abc import abstractmethod
-import tensorflow as tf
+import tensorflow.compat.v1 as tf
 
 BOX_ENCODINGS = 'box_encodings'
 CLASS_PREDICTIONS_WITH_BACKGROUND = 'class_predictions_with_background'

research/object_detection/core/class_agnostic_nms_test.py

@@ -14,7 +14,7 @@
 # ==============================================================================
 """Tests for google3.third_party.tensorflow_models.object_detection.core.class_agnostic_nms."""
 from absl.testing import parameterized
-import tensorflow as tf
+import tensorflow.compat.v1 as tf
 from object_detection.core import post_processing
 from object_detection.core import standard_fields as fields
 from object_detection.utils import test_case

research/object_detection/core/freezable_batch_norm.py

@@ -14,7 +14,7 @@
 # ==============================================================================
 
 """A freezable batch norm layer that uses Keras batch normalization."""
-import tensorflow as tf
+import tensorflow.compat.v1 as tf
 
 
 class FreezableBatchNorm(tf.keras.layers.BatchNormalization):

research/object_detection/core/freezable_batch_norm_test.py

@@ -20,7 +20,7 @@ from __future__ import print_function
 
 import numpy as np
 from six.moves import zip
-import tensorflow as tf
+import tensorflow.compat.v1 as tf
 
 
 from object_detection.core import freezable_batch_norm

research/object_detection/core/keypoint_ops.py

@@ -20,7 +20,7 @@ where the last dimension holds rank 2 tensors of the form [y, x] representing
 the coordinates of the keypoint.
 """
 import numpy as np
-import tensorflow as tf
+import tensorflow.compat.v1 as tf
 
 
 def scale(keypoints, y_scale, x_scale, scope=None):

research/object_detection/core/keypoint_ops_test.py

@@ -15,7 +15,7 @@
 
 """Tests for object_detection.core.keypoint_ops."""
 import numpy as np
-import tensorflow as tf
+import tensorflow.compat.v1 as tf
 
 from object_detection.core import keypoint_ops
 from object_detection.utils import test_case

research/object_detection/core/losses.py

@@ -32,15 +32,11 @@ from __future__ import print_function
 
 import abc
 import six
-import tensorflow as tf
-from tensorflow.contrib import slim as contrib_slim
-
+import tensorflow.compat.v1 as tf
 from object_detection.core import box_list
 from object_detection.core import box_list_ops
 from object_detection.utils import ops
 
-slim = contrib_slim
-
 
 class Loss(six.with_metaclass(abc.ABCMeta, object)):
   """Abstract base class for loss functions."""

research/object_detection/core/losses_test.py

@@ -22,7 +22,7 @@ import math
 
 import numpy as np
 from six.moves import zip
-import tensorflow as tf
+import tensorflow.compat.v1 as tf
 
 from object_detection.core import box_list
 from object_detection.core import losses

research/object_detection/core/matcher.py

@@ -37,7 +37,7 @@ from __future__ import print_function
 
 import abc
 import six
-import tensorflow as tf
+import tensorflow.compat.v1 as tf
 
 from object_detection.utils import ops