I can take this issue.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/7f6a0145ae3deb8920771b2a2347af5f5c91aedd

commit 7f6a0145ae3deb8920771b2a2347af5f5c91aedd
Author: tianyuwang <tianyuwang@google.com>
Date: Fri Apr 01 18:48:05 2016

[chromecast] Pass media task runner to MediaPipelineBackendManager.

This required making MediaPipelineBackendManager non-singleton and
passed around wherever required.

BUG= 597450 

Review URL: https://codereview.chromium.org/1845783002

Cr-Commit-Position: refs/heads/master@{#384643}

[modify] https://crrev.com/7f6a0145ae3deb8920771b2a2347af5f5c91aedd/chromecast/browser/cast_browser_main_parts.cc
[modify] https://crrev.com/7f6a0145ae3deb8920771b2a2347af5f5c91aedd/chromecast/browser/cast_browser_main_parts.h
[modify] https://crrev.com/7f6a0145ae3deb8920771b2a2347af5f5c91aedd/chromecast/browser/cast_content_browser_client.cc
[modify] https://crrev.com/7f6a0145ae3deb8920771b2a2347af5f5c91aedd/chromecast/browser/cast_content_browser_client.h
[modify] https://crrev.com/7f6a0145ae3deb8920771b2a2347af5f5c91aedd/chromecast/media/audio/cast_audio_manager.cc
[modify] https://crrev.com/7f6a0145ae3deb8920771b2a2347af5f5c91aedd/chromecast/media/audio/cast_audio_manager.h
[modify] https://crrev.com/7f6a0145ae3deb8920771b2a2347af5f5c91aedd/chromecast/media/audio/cast_audio_manager_factory.cc
[modify] https://crrev.com/7f6a0145ae3deb8920771b2a2347af5f5c91aedd/chromecast/media/audio/cast_audio_manager_factory.h
[modify] https://crrev.com/7f6a0145ae3deb8920771b2a2347af5f5c91aedd/chromecast/media/audio/cast_audio_output_stream_unittest.cc
[modify] https://crrev.com/7f6a0145ae3deb8920771b2a2347af5f5c91aedd/chromecast/media/cma/backend/media_pipeline_backend_manager.cc
[modify] https://crrev.com/7f6a0145ae3deb8920771b2a2347af5f5c91aedd/chromecast/media/cma/backend/media_pipeline_backend_manager.h
[modify] https://crrev.com/7f6a0145ae3deb8920771b2a2347af5f5c91aedd/chromecast/media/cma/backend/media_pipeline_backend_wrapper.cc
[modify] https://crrev.com/7f6a0145ae3deb8920771b2a2347af5f5c91aedd/chromecast/media/cma/backend/media_pipeline_backend_wrapper.h

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/256cb1b61f5f9658536b083ff2862152348cf0a3

commit 256cb1b61f5f9658536b083ff2862152348cf0a3
Author: tianyuwang <tianyuwang@google.com>
Date: Sat Apr 02 00:34:53 2016

Revert of [chromecast] Pass media task runner to MediaPipelineBackendManager. (patchset #8 id:140001 of https://codereview.chromium.org/1845783002/ )

Reason for revert:
Broke chromecast.  Will reland it after that's fixed.

Original issue's description:
> [chromecast] Pass media task runner to MediaPipelineBackendManager.
>
> This required making MediaPipelineBackendManager non-singleton and
> passed around wherever required.
>
> BUG= 597450 
>
> Committed: https://crrev.com/7f6a0145ae3deb8920771b2a2347af5f5c91aedd
> Cr-Commit-Position: refs/heads/master@{#384643}

TBR=alokp@chromium.org,halliwell@chromium.org,kmackay@chromium.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG= 597450 

Review URL: https://codereview.chromium.org/1855633002

Cr-Commit-Position: refs/heads/master@{#384756}

[modify] https://crrev.com/256cb1b61f5f9658536b083ff2862152348cf0a3/chromecast/browser/cast_browser_main_parts.cc
[modify] https://crrev.com/256cb1b61f5f9658536b083ff2862152348cf0a3/chromecast/browser/cast_browser_main_parts.h
[modify] https://crrev.com/256cb1b61f5f9658536b083ff2862152348cf0a3/chromecast/browser/cast_content_browser_client.cc
[modify] https://crrev.com/256cb1b61f5f9658536b083ff2862152348cf0a3/chromecast/browser/cast_content_browser_client.h
[modify] https://crrev.com/256cb1b61f5f9658536b083ff2862152348cf0a3/chromecast/media/audio/cast_audio_manager.cc
[modify] https://crrev.com/256cb1b61f5f9658536b083ff2862152348cf0a3/chromecast/media/audio/cast_audio_manager.h
[modify] https://crrev.com/256cb1b61f5f9658536b083ff2862152348cf0a3/chromecast/media/audio/cast_audio_manager_factory.cc
[modify] https://crrev.com/256cb1b61f5f9658536b083ff2862152348cf0a3/chromecast/media/audio/cast_audio_manager_factory.h
[modify] https://crrev.com/256cb1b61f5f9658536b083ff2862152348cf0a3/chromecast/media/audio/cast_audio_output_stream_unittest.cc
[modify] https://crrev.com/256cb1b61f5f9658536b083ff2862152348cf0a3/chromecast/media/cma/backend/media_pipeline_backend_manager.cc
[modify] https://crrev.com/256cb1b61f5f9658536b083ff2862152348cf0a3/chromecast/media/cma/backend/media_pipeline_backend_manager.h
[modify] https://crrev.com/256cb1b61f5f9658536b083ff2862152348cf0a3/chromecast/media/cma/backend/media_pipeline_backend_wrapper.cc
[modify] https://crrev.com/256cb1b61f5f9658536b083ff2862152348cf0a3/chromecast/media/cma/backend/media_pipeline_backend_wrapper.h

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/c7e35d80cffa26c4ddc76ba6f71fd3127dccec31

commit c7e35d80cffa26c4ddc76ba6f71fd3127dccec31
Author: tianyuwang <tianyuwang@google.com>
Date: Wed Apr 06 21:24:18 2016

[chromecast] Pass media task runner to MediaPipelineBackendManager.

BUG= 597450 

Review URL: https://codereview.chromium.org/1858803002

Cr-Commit-Position: refs/heads/master@{#385556}

[modify] https://crrev.com/c7e35d80cffa26c4ddc76ba6f71fd3127dccec31/chromecast/browser/cast_browser_main_parts.cc
[modify] https://crrev.com/c7e35d80cffa26c4ddc76ba6f71fd3127dccec31/chromecast/browser/cast_browser_main_parts.h
[modify] https://crrev.com/c7e35d80cffa26c4ddc76ba6f71fd3127dccec31/chromecast/browser/cast_content_browser_client.cc
[modify] https://crrev.com/c7e35d80cffa26c4ddc76ba6f71fd3127dccec31/chromecast/browser/cast_content_browser_client.h
[modify] https://crrev.com/c7e35d80cffa26c4ddc76ba6f71fd3127dccec31/chromecast/media/audio/cast_audio_manager.cc
[modify] https://crrev.com/c7e35d80cffa26c4ddc76ba6f71fd3127dccec31/chromecast/media/audio/cast_audio_manager.h
[modify] https://crrev.com/c7e35d80cffa26c4ddc76ba6f71fd3127dccec31/chromecast/media/audio/cast_audio_manager_factory.cc
[modify] https://crrev.com/c7e35d80cffa26c4ddc76ba6f71fd3127dccec31/chromecast/media/audio/cast_audio_manager_factory.h
[modify] https://crrev.com/c7e35d80cffa26c4ddc76ba6f71fd3127dccec31/chromecast/media/audio/cast_audio_output_stream_unittest.cc
[modify] https://crrev.com/c7e35d80cffa26c4ddc76ba6f71fd3127dccec31/chromecast/media/cma/backend/media_pipeline_backend_manager.cc
[modify] https://crrev.com/c7e35d80cffa26c4ddc76ba6f71fd3127dccec31/chromecast/media/cma/backend/media_pipeline_backend_manager.h
[modify] https://crrev.com/c7e35d80cffa26c4ddc76ba6f71fd3127dccec31/chromecast/media/cma/backend/media_pipeline_backend_wrapper.cc
[modify] https://crrev.com/c7e35d80cffa26c4ddc76ba6f71fd3127dccec31/chromecast/media/cma/backend/media_pipeline_backend_wrapper.h