Cast: Ensure limited number of frames in flight

This cl makes sure that we don't have more than the max allowed frames in flight.
In addition, behavior when sender starts before receiver is
 modified such that the sender will keep re-sending the first key frame instead of
generating (encoding) a new key frame.

A test and a DCHECK were added to ensure desired functionality.  


BUG=347194

Review URL: https://codereview.chromium.org/183093005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@254302 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 254302
Remove EnableThemeSupportOnAllWindowStations

If we don't return early on failure we may crash due to sandbox conflicts on Win 8.1.

BUG=347849
R=cpu,jam
TBR=jam

Review URL: https://codereview.chromium.org/184393005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@254303 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 254303