Implement external stencil for Android WebView

cc/output/gl_renderer.cc

 // Copyright 2010 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.
 
 #include "cc/output/gl_renderer.h"
 
 #include <stddef.h>
 #include <stdint.h>
 
 #include <algorithm>
@@ skipping 2903 matching lines @@
   frame->current_texture = texture;
 
   return BindFramebufferToTexture(frame, texture, viewport_rect);
 }
 
 void GLRenderer::BindFramebufferToOutputSurface(DrawingFrame* frame) {
   current_framebuffer_lock_ = nullptr;
   output_surface_->BindFramebuffer();
 
   if (output_surface_->HasExternalStencilTest()) {
+    output_surface_->ApplyExternalStencil();
     SetStencilEnabled(true);
-    gl_->StencilFunc(GL_EQUAL, 1, 1);
   } else {
     SetStencilEnabled(false);
   }
 }
 
 bool GLRenderer::BindFramebufferToTexture(DrawingFrame* frame,
                                           const ScopedResource* texture,
                                           const gfx::Rect& target_rect) {
   DCHECK(texture->id());
 
@@ skipping 645 matching lines @@
       texture_id = pending_overlay_resources_.back()->texture_id();
     }
 
     context_support_->ScheduleOverlayPlane(
         overlay.plane_z_order, overlay.transform, texture_id,
         ToNearestRect(overlay.display_rect), overlay.uv_rect);
   }
 }
 
 }  // namespace cc