Plumb the partial swap though image transport.

ui/gfx/gl/gl_surface.cc

Index: ui/gfx/gl/gl_surface.cc
diff --git a/ui/gfx/gl/gl_surface.cc b/ui/gfx/gl/gl_surface.cc
index 9276d00d6d061a814d64ac3dd5b749e1d9cab7c6..832925578d98c1bcec349ed03782fea4fc43dcf0 100644
--- a/ui/gfx/gl/gl_surface.cc
+++ b/ui/gfx/gl/gl_surface.cc
@@ -91,7 +91,9 @@ bool GLSurface::Resize(const gfx::Size& size) {
 }
 
 std::string GLSurface::GetExtensions() {
-  DCHECK_EQ(GetCurrent(), this);
+  // Use of GLSurfaceAdapter class means that we can't compare
+  // GetCurrent() and this directly.
+  DCHECK_EQ(GetCurrent()->GetHandle(), GetHandle());
   return std::string("");
 }
 
@@ -164,6 +166,14 @@ bool GLSurfaceAdapter::SwapBuffers() {
   return surface_->SwapBuffers();
 }
 
+bool GLSurfaceAdapter::PostSubBuffer(int x, int y, int width, int height) {
+  return surface_->PostSubBuffer(x, y, width, height);
+}
+
+std::string GLSurfaceAdapter::GetExtensions() {
+  return surface_->GetExtensions();
+}
+
 gfx::Size GLSurfaceAdapter::GetSize() {
   return surface_->GetSize();
 }