cc: Use the correct internal format for glCopyTexImage2D calls.

cc/test/pixel_test_output_surface.cc

Index: cc/test/pixel_test_output_surface.cc
diff --git a/cc/test/pixel_test_output_surface.cc b/cc/test/pixel_test_output_surface.cc
index b13b46d314307b2111f2b619b873d0a78133bb70..b818a0828ae230008adde7aa7f30982f6810fd91 100644
--- a/cc/test/pixel_test_output_surface.cc
+++ b/cc/test/pixel_test_output_surface.cc
@@ -7,6 +7,7 @@
 #include <utility>
 
 #include "cc/output/output_surface_client.h"
+#include "third_party/khronos/GLES2/gl2.h"
 #include "ui/gfx/transform.h"
 
 namespace cc {
@@ -54,4 +55,11 @@ void PixelTestOutputSurface::SwapBuffers(CompositorFrame* frame) {
   client_->DidSwapBuffers();
 }
 
+uint32_t PixelTestOutputSurface::GetFramebufferCopyTextureFormat() {
+  // This format will work if the |context_provider| has an RGB or RGBA
+  // framebuffer. For now assume tests do not want/care about alpha in
+  // the root render pass.
+  return GL_RGB;
+}
+
 }  // namespace cc