gpu: Add CHROMIUM_copy_image extension.

ui/gl/gl_image_stub.h

Index: ui/gl/gl_image_stub.h
diff --git a/ui/gl/gl_image_stub.h b/ui/gl/gl_image_stub.h
index 30da6c76dc887f140fae487572f26f5805e38340..19aa421d0c56eddf89916a8b34462b04be45b36f 100644
--- a/ui/gl/gl_image_stub.h
+++ b/ui/gl/gl_image_stub.h
@@ -27,6 +27,11 @@ class GL_EXPORT GLImageStub : public GLImage {
   bool CopyTexSubImage(unsigned target,
                        const gfx::Point& offset,
                        const gfx::Rect& rect) override;
+  bool CopySubImageData(unsigned texture_id,
+                        const gfx::Point& offset,
+                        const gfx::Rect& rect,
+                        GLFence* in_fence,
+                        GLFence* out_fence) override;
   bool ScheduleOverlayPlane(gfx::AcceleratedWidget widget,
                             int z_order,
                             gfx::OverlayTransform transform,