Offset scissor and viewport when using SetDrawRectangle on surface.

gpu/ipc/service/direct_composition_surface_win.h

Index: gpu/ipc/service/direct_composition_surface_win.h
diff --git a/gpu/ipc/service/direct_composition_surface_win.h b/gpu/ipc/service/direct_composition_surface_win.h
index 831bbe938b5d247775b208087d68469d3b91a93f..28fbc76dbc9950c3a4cec2c6d37cc211cd4e5a4d 100644
--- a/gpu/ipc/service/direct_composition_surface_win.h
+++ b/gpu/ipc/service/direct_composition_surface_win.h
@@ -50,6 +50,7 @@ class GPU_EXPORT DirectCompositionSurfaceWin : public gl::GLSurfaceEGL {
   bool OnMakeCurrent(gl::GLContext* context) override;
   bool SupportsSetDrawRectangle() const override;
   bool SetDrawRectangle(const gfx::Rect& rect) override;
+  gfx::Vector2d GetDrawOffset() const override;
 
   bool Initialize(std::unique_ptr<gfx::VSyncProvider> vsync_provider);
 
@@ -95,6 +96,8 @@ class GPU_EXPORT DirectCompositionSurfaceWin : public gl::GLSurfaceEGL {
   std::unique_ptr<gfx::VSyncProvider> vsync_provider_;
   std::vector<Overlay> pending_overlays_;
 
+  gfx::Vector2d draw_offset_;
+
   base::win::ScopedComPtr<ID3D11Device> d3d11_device_;
   base::win::ScopedComPtr<IDCompositionDevice2> dcomp_device_;
   base::win::ScopedComPtr<IDCompositionTarget> dcomp_target_;