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* Add session hook for benchmark metric logging.

Current hook is very similar as the LoggingTensorHook. Some of the
function are directly copied since the original one was not
exposed for import. We should seek to eventually move this code to
core when it is mature enough.

* Update metric_hook to use LoggingTensorHook as base.

The existing hook is similar enough to LoggingTensorHook, and
we should eliminate duplicate as much as possible.

* Address review comment.

1. Update global step tensor handle.
2. Update tests.
3. Update document.

* Update tests for py3.

* Fix lint error

* Glint everything

* Adding rcfile and pylinting

* Extra newline

* Few last lints

Use util functions hooks_helper and parser in mnist and wide_deep, and rename epochs_between_eval (from epochs_per_eval) (#3650)

* Update resnet with logging utils

* intermediate commit

* commit before rebase from master

* Add tests of ExamplePerSecondHook

* Done with test

* Fix a style nit

* Fix a style nit

* Removing dependency on tf.test

* New lines

* Adding logging utils

* restore utils

* delete old file

* update inputs and docstrings

* Update import and fix typos

* Fix formatting and comments

* Update tests