Fix a problem that external surface might be released too early

In https://codereview.chromium.org/182403002/, we modified the logic to call OnMediaResourcesRealsed().
For MSE, each time a video decoder is released, this function will get called. This may happen when config change happens.
However, we shouldn't release the external surface during config changes.
This CL changes the logic to release the external surface only after MediaPlayerAndroid::Release() is called.

TBR=yfriedman

Review URL: https://codereview.chromium.org/185263004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@254619 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 254619