Fix not signaling in MediaPlayerGStreamer::SetupGLContext() if ContextProvider::BindToCurrentThread() fails.
Fix not signaling in MediaPlayerGStreamer::SetupGLContext() if ContextProvider::BindToCurrentThread() fails.

Also some refactoring to move mutex guards under local scope.

lihui7115/ChromiumGStreamerBackend,lihui7115/ChromiumGStreamerBackend,lihui7115/ChromiumGStreamerBackend,lihui7115/ChromiumGStreamerBackend,lihui7115/ChromiumGStreamerBackend,lihui7115/ChromiumGStreamerBackend,lihui7115/ChromiumGStreamerBackend,lihui7115/ChromiumGStreamerBackend,lihui7115/ChromiumGStreamerBackend