WebMediaPlayer{Android,Impl}: use RenderFrameObserver instead of ML::DestructionObserver/RenderViewObserver.

RenderThreadImpl is torn down before the main thread's MessageLoop is, and some
of WebMediaPlayerAndroid's dependencies require the render thread to still be
alive, so move its tear-down to earlier in the process.
This is the Android version of r240125 which fixed the same bug in
WebMediaPlayerImpl, but forgot that WebMediaPlayerAndroid is a fork.

Since RenderViewObserver is apparently out of favor nowadays, use RenderFrameObserver.

BUG=338393,304967,338481

[Previously committed PS#3 as r248115 and rolled back in r248128]

R=cevans@chromium.org, jam@chromium.org, piman@chromium.org, scherkus@chromium.org

Review URL: https://codereview.chromium.org/137243005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@248321 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 248321