media: Allow config change between clear and encrypted streams

In the demuxer, we allow DecryptConfig change upon config change,
including but not limited to:
- switching between clear and encrypted
- encryption scheme change

Media Renderer implementation should support such changes. The detailed
requirement from the spec's perspective is tracked at:
https://github.com/w3c/encrypted-media/issues/251

Currently the default media Renderer (RendererImpl) supports switching
from encrypted to clear, because:
- Decrypt-and-decode mode: Decrypting{Audio|Video}Decoder supports clear
  buffer.
- Decrypt-only mode: DecryptingDemuxerStream supports clear buffer.

However, switching from clear to encrypted is not supported in
RendererImpl, because the clear decoder doesn't support decryption. This
will be fixed in a later CL.

BUG=597443
TEST=Updated pipeline_integration_tests.

Review-Url: https://codereview.chromium.org/2543623003
Cr-Commit-Position: refs/heads/master@{#451212}

• chrome/browser/media/encrypted_media_browsertest.cc[diff]
• chrome/browser/media/media_browsertest.cc[diff]
• chrome/browser/media/media_browsertest.h[diff]
• content/browser/media/encrypted_media_browsertest.cc[diff]
• content/browser/media/media_browsertest.cc[diff]
• content/browser/media/media_browsertest.h[diff]
• content/browser/media/media_source_browsertest.cc[diff]
• content/renderer/media/cdm/ppapi_decryptor.cc[diff]
• content/renderer/pepper/content_decryptor_delegate.cc[diff]
• media/cdm/ppapi/external_clear_key/clear_key_cdm.cc[diff]
• media/filters/decoder_stream.h[diff]
• media/filters/decrypting_audio_decoder.cc[diff]
• media/filters/decrypting_audio_decoder_unittest.cc[diff]
• media/filters/decrypting_demuxer_stream.cc[diff]
• media/filters/decrypting_demuxer_stream_unittest.cc[diff]
• media/filters/decrypting_video_decoder.cc[diff]
• media/filters/decrypting_video_decoder_unittest.cc[diff]
• media/filters/source_buffer_stream.cc[diff]
• media/test/data/eme_player.html[diff]
• media/test/data/eme_player_js/globals.js[diff]
• media/test/data/eme_player_js/test_config.js[diff]
• media/test/data/mse_config_change.html[diff]
• media/test/pipeline_integration_test.cc[diff]