Offset scissor and viewport when using SetDrawRectangle on surface.

ui/gl/gl_surface_stub.h

Index: ui/gl/gl_surface_stub.h
diff --git a/ui/gl/gl_surface_stub.h b/ui/gl/gl_surface_stub.h
index 860f989667c047e93ec188a1a04b1fef406ae68b..87f5565582cb86c1e70620282fb365c93a07c6ee 100644
--- a/ui/gl/gl_surface_stub.h
+++ b/ui/gl/gl_surface_stub.h
@@ -16,6 +16,10 @@ class GL_EXPORT GLSurfaceStub : public GLSurface {
   void SetSize(const gfx::Size& size) { size_ = size; }
   void set_buffers_flipped(bool flipped) { buffers_flipped_ = flipped; }
 
+  void set_supports_draw_rectangle(bool support) {
+    supports_draw_rectangle_ = support;
+  }
+
   // Implement GLSurface.
   void Destroy() override;
   bool Resize(const gfx::Size& size,
@@ -27,6 +31,8 @@ class GL_EXPORT GLSurfaceStub : public GLSurface {
   void* GetHandle() override;
   bool BuffersFlipped() const override;
   GLSurfaceFormat GetFormat() override;
+  bool SupportsSetDrawRectangle() const override;
+  gfx::Vector2d GetDrawOffset() const override;
 
  protected:
   ~GLSurfaceStub() override;
@@ -34,6 +40,7 @@ class GL_EXPORT GLSurfaceStub : public GLSurface {
  private:
   gfx::Size size_;
   bool buffers_flipped_ = false;
+  bool supports_draw_rectangle_ = false;
 };
 
 }  // namespace gl