Reland "Refactor audio manager for Android to avoid heavy tasks at startup"

Original CL: https://codereview.chromium.org/110173003/.

Refactor audio manager for Android to avoid heavy tasks at startup.

Main goal of this CL is to avoid all demanding tasks (e.g. initiate audio routing, detect BT devices etc.) at Chrome startup.

All we do now is to populate the list of available devices. BT support has been removed but will be added in an upcoming CL.

NOTRY=True
TBR=bulach, tommi
BUG=324464
TEST=media_unittests --gtest-filter=AudioAndroid*

Review URL: https://codereview.chromium.org/117073002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@241247 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 241247