Revert 256666 "Use the default dispatcher where possible for nes..."

> Use the default dispatcher where possible for nested message loops.
> 
> * SimpleMessageBoxViews is no longer MessagePumpDispatcher.
>   The default dispatcher is used instead, and QuitNestedMessageLoop()
>   is called to terminate the loop instead of returning
>   POST_DISPATCH_QUIT_LOOP from the Dispatch() override.
> 
> This is a partial re-land of crrev.com/253723
> 
> BUG=351393
> TEST=trybot and manual testing on Chrome OS.
> R=msw@chromium.org, sadrul@chromium.org, sky@chromium.org
> 
> Review URL: https://codereview.chromium.org/197903002

TBR=hshi@chromium.org

Review URL: https://codereview.chromium.org/198013004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@256693 0039d316-1c4b-4281-b951-d872f2087c98
Reland "Avoid hitting the thread check when WebRtcAudioRenderer is going away"

This relands r255158 without including the changes to webrtc_audio_renderer.cc.
This prevents audio loss from occuring in other WebRTC apps.

Setting notry=true because this is essentially just reverting the revert I made about an hour ago.


> Avoid hitting the thread check when WebRtcAudioRenderer is going away.
>
> We need to reset the render_thread_checker and render_converter_ when the WebRtcAudioRenderer is going away.
>
> NOTRY=true
>
> BUG=264611
> TEST=manual test webrtc with --enable-audio-track-processor

NOTRY=true
BUG=351895,264611

Review URL: https://codereview.chromium.org/198303002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@256694 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 256694