Allow to have a transparent UA dependent background.

cc/layers/picture_layer_impl.cc

 // 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.
 
 #include "cc/layers/picture_layer_impl.h"
 
 #include <stddef.h>
 #include <stdint.h>
 
 #include <algorithm>
@@ skipping 307 matching lines @@
                        texture_rect, draw_info.resource_size(),
                        draw_info.contents_swizzled(), nearest_neighbor_);
           ValidateQuadResources(quad);
           iter->draw_info().set_was_ever_used_to_draw();
           has_draw_quad = true;
           break;
         }
         case TileDrawInfo::SOLID_COLOR_MODE: {
           SolidColorDrawQuad* quad =
               render_pass->CreateAndAppendDrawQuad<SolidColorDrawQuad>();
-          quad->SetNew(shared_quad_state, geometry_rect, visible_geometry_rect,
-                       draw_info.solid_color(), false);
+
+          // At the beginning of the for loop above, opaque_rect is defined
+          // against contents_opaque(). If it was actually the case then use it
+          // otherwise use quad->SetNew which configure opaque_rect on other
+          // condition.
+          if (contents_opaque()) {
+            quad->SetAll(shared_quad_state, geometry_rect, opaque_rect,
+                         visible_geometry_rect, false, draw_info.solid_color(),
+                         false);
+          } else {
+            quad->SetNew(shared_quad_state, geometry_rect,
+                         visible_geometry_rect, draw_info.solid_color(), false);
+          }

[trchen, 2016/03/08 01:57:21]

Why is this change needed? This only changes the behavior when a layer is
opaque, but what the thing you want to change is how non-opaque pages being
handled.

           ValidateQuadResources(quad);
           iter->draw_info().set_was_ever_used_to_draw();
           has_draw_quad = true;
           break;
         }
         case TileDrawInfo::OOM_MODE:
           break;  // Checkerboard.
       }
     }
 
@@ skipping 919 matching lines @@
 
 bool PictureLayerImpl::IsOnActiveOrPendingTree() const {
   return !layer_tree_impl()->IsRecycleTree();
 }
 
 bool PictureLayerImpl::HasValidTilePriorities() const {
   return IsOnActiveOrPendingTree() && IsDrawnRenderSurfaceLayerListMember();
 }
 
 }  // namespace cc