Implement client side PBOs for glReadPixel

Use PBOs in gl_helper
swizzle bytes on gpu
flip vertically on gpu
remove gl_helper_thread

Implements GLHelper::CropScaleReadbackAndCleanTexture() to be non-blocking in the client by using shared memory combined with a query (not requiring actual GL PBO support, which would not be available on Android). 


Review URL: https://chromiumcodereview.appspot.com/12892005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@191737 0039d316-1c4b-4281-b951-d872f2087c98

content/browser/renderer_host/image_transport_factory.cc

@@ -464,15 +464,9 @@ class GpuProcessTransportFactory
   virtual GLHelper* GetGLHelper() OVERRIDE {
     if (!gl_helper_.get()) {
       CreateSharedContextLazy();
-      WebKit::WebGraphicsContext3D* context_for_main_thread =
+      WebGraphicsContext3DCommandBufferImpl* context_for_main_thread =
           shared_contexts_main_thread_->Context3d();
-      WebKit::WebGraphicsContext3D* context_for_thread =
-          CreateOffscreenContext();
-      if (!context_for_thread)
-        return NULL;
-
-      gl_helper_.reset(new GLHelper(context_for_main_thread,
-                                    context_for_thread));
+      gl_helper_.reset(new GLHelper(context_for_main_thread));
     }
     return gl_helper_.get();
   }

content/browser/renderer_host/image_transport_factory_android.cc

@@ -161,7 +161,7 @@ void CmdBufferImageTransportFactory::ReleaseTexture(
 
 GLHelper* CmdBufferImageTransportFactory::GetGLHelper() {
   if (!gl_helper_.get())
-    gl_helper_.reset(new GLHelper(GetContext3D(), NULL));
+    gl_helper_.reset(new GLHelper(context_.get()));
 
   return gl_helper_.get();
 }