gpu: Add CHROMIUM_copy_image extension.

ui/gl/gl_image_glx.h

Index: ui/gl/gl_image_glx.h
diff --git a/ui/gl/gl_image_glx.h b/ui/gl/gl_image_glx.h
index 2b7604a14d31a5f54934df115b8e485a3f689d82..b4031450d60845ae8d4a46f300950deeb7a0d174 100644
--- a/ui/gl/gl_image_glx.h
+++ b/ui/gl/gl_image_glx.h
@@ -31,6 +31,11 @@ class GL_EXPORT GLImageGLX : 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,