Previously we had two subclasses of MediaCodecBridgeImpl,
VideoCodecBridge and AudioCodecBridge, which have become unnecessary.
For simplicity and ease of mocking, now we just have
MediaCodecBridgeImpl.

This CL also includes various cleanups, including:
* MediaCodecBridge factories return unique_ptrs.
* Remove some unused MCB functions.
* Use the java enum generator where possible to sync native and java
  enums.
* Collapsing DEQUEUE_OUTPUT_TRY_AGAIN and DEQUEUE_INPUT_TRY_AGAIN into
  a single TRY_AGAIN (like MediaCodec).
* Remove size params from isAdaptivePlaybackSupported() because they
  weren't used.
* Localizing codec to mime type conversions to MediaCodecUtil.
* Passing mime strings to MediaCodecUtil::CanDecode() instead of an
  ad-hoc codec name string.

BUG=691828
TEST=existing tests
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:linux_optional_gpu_tests_rel;master.tryserver.chromium.mac:mac_optional_gpu_tests_rel;master.tryserver.chromium.win:win_optional_gpu_tests_rel

Review-Url: https://codereview.chromium.org/2697643003
Cr-Commit-Position: refs/heads/master@{#452334}