Implement external stencil for Android WebView

cc/output/output_surface.h

 // Copyright 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CC_OUTPUT_OUTPUT_SURFACE_H_
 #define CC_OUTPUT_OUTPUT_SURFACE_H_
 
 #include <deque>
 
 #include "base/macros.h"
@@ skipping 73 matching lines @@
     bool can_force_reclaim_resources;
     // True if sync points for resources are needed when swapping delegated
     // frames.
     bool delegated_sync_points_required;
   };
 
   const Capabilities& capabilities() const {
     return capabilities_;
   }
 
   virtual bool HasExternalStencilTest() const;

[aelias_OOO_until_Jul13, 2016/01/06 23:43:36]

Maybe this could be replaced by a bool returned from ApplyExternalStencil?

[boliu, 2016/01/07 15:42:43]

Then there is no way to do this DCHECK in software_renderer that there is no
external stencil:
https://code.google.com/p/chromium/codesearch#chromium/src/cc/output/software...

+  virtual void ApplyExternalStencil();
 
   // Obtain the 3d context or the software device associated with this output
   // surface. Either of these may return a null pointer, but not both.
   // In the event of a lost context, the entire output surface should be
   // recreated.
   ContextProvider* context_provider() const { return context_provider_.get(); }
   ContextProvider* worker_context_provider() const {
     return worker_context_provider_.get();
   }
   SoftwareOutputDevice* software_device() const {
@@ skipping 92 matching lines @@
   bool external_stencil_test_enabled_;
 
   base::WeakPtrFactory<OutputSurface> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(OutputSurface);
 };
 
 }  // namespace cc
 
 #endif  // CC_OUTPUT_OUTPUT_SURFACE_H_