rendering_helper - Flush the GL commands after rendering to FBO.

We need this synchronization before we can return the texture to the decoder.

BUG=391234
TEST=Run the vda_unittest on lumpy

Review URL: https://codereview.chromium.org/371593002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@285228 0039d316-1c4b-4281-b951-d872f2087c98

content/common/gpu/media/rendering_helper.cc

@@ -363,6 +363,10 @@ void RenderingHelper::RenderThumbnail(uint32 texture_target,
   GLSetViewPort(area);
   RenderTexture(texture_target, texture_id);
   glBindFramebufferEXT(GL_FRAMEBUFFER, 0);
+
+  // Need to flush the GL commands before we return the tnumbnail texture to
+  // the decoder.
+  glFlush();
   ++frame_count_;
 }