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This CL is the first step towards mojification of GpuJpegDecodeAccelerator(GJDA)
and GpuJpegDecodeAcceleratorHost(GJDAH).

1. Defines media::BitstreamBuffer and AcceleratedJpegDecoderMsg_Decode_Params for mojo.
2. GJDA and GJDAH implement these interfaces. Currently, these implementations are empty.

BUG=699255
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.android:android_optional_gpu_tests_rel;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/2905823002
Cr-Commit-Position: refs/heads/master@{#476712}