Partial swap implementation for surfaceless

ui/gl/gl_surface_ozone.cc

Index: ui/gl/gl_surface_ozone.cc
diff --git a/ui/gl/gl_surface_ozone.cc b/ui/gl/gl_surface_ozone.cc
index 0c30c20ba0a578206ae85103637afcfea4c94b18..e257364e50bcf39d8ee591a2a2a7e1a1a09e5c64 100644
--- a/ui/gl/gl_surface_ozone.cc
+++ b/ui/gl/gl_surface_ozone.cc
@@ -138,6 +138,12 @@ class GL_EXPORT GLSurfaceOzoneSurfaceless : public SurfacelessEGL {
   virtual VSyncProvider* GetVSyncProvider() OVERRIDE {
     return vsync_provider_.get();
   }
+  virtual bool SupportsPostSubBuffer() OVERRIDE { return true; }
+  virtual bool PostSubBuffer(int x, int y, int width, int height) OVERRIDE {
+    // The actual sub buffer handling is handled at higher layers.
+    SwapBuffers();
+    return true;
+  }
 
  private:
   virtual ~GLSurfaceOzoneSurfaceless() {