gpu rtc video: Don't destroy a video texture in the destructor until it's returned.

gpu rtc video: Don't destroy a video texture in the destructor until it's returned.

This CL fixes the bug that RVD makes the compositor get following gl error.
[20074:20074:0317/145233:1532049594488:ERROR:gles2_cmd_decoder.cc(10071)]
[.Compositor-0x731c2a2e9a0]GL ERROR :GL_INVALID_OPERATION : glConsumeTextureCHROMIUM: invalid mailbox name

Currently, RTCVideoDecoder deletes all textures, even if some textures are
used by the clients. This CL makes "release callback" be able to delete remained
textures even after RTCVideoDecoder is destructed.

This pattern is very similar that GpuVideoDecoder, accelerated 2d canvas and
WebGL release remained mailboxes. See GpuVideoDecoder.

In addition, this CL removes |dismissed_picture_buffers_| because we can know
Set{|dismissed_picture_buffers_|} by Sets Algebra A - B;
Set{|picture_buffers_at_display_|} - Set{|assigned_picture_buffers_|}.

TEST=Run http://apprtc.appspot.com/?debug=loopback on Nexus 5.

BUG=350925, 344393

Review URL: https://codereview.chromium.org/202023006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@259065 0039d316-1c4b-4281-b951-d872f2087c98