Add channel_layout() and sample_rate() to AudioBuffer.

BUG=347270

Review URL: https://codereview.chromium.org/187023004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@258201 0039d316-1c4b-4281-b951-d872f2087c98

• content/renderer/pepper/content_decryptor_delegate.cc[diff]
• content/renderer/pepper/content_decryptor_delegate.h[diff]
• media/base/audio_buffer.cc[diff]
• media/base/audio_buffer.h[diff]
• media/base/audio_buffer_queue_unittest.cc[diff]
• media/base/audio_buffer_unittest.cc[diff]
• media/base/audio_splicer.cc[diff]
• media/base/audio_splicer.h[diff]
• media/base/audio_splicer_unittest.cc[diff]
• media/base/test_helpers.cc[diff]
• media/base/test_helpers.h[diff]
• media/filters/audio_renderer_algorithm_unittest.cc[diff]
• media/filters/audio_renderer_impl_unittest.cc[diff]
• media/filters/decrypting_audio_decoder_unittest.cc[diff]
• media/filters/ffmpeg_audio_decoder.cc[diff]
• media/filters/opus_audio_decoder.cc[diff]