Force use of and cache render surface.

cc/trees/occlusion_tracker.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/trees/occlusion_tracker.h"
 
 #include <stddef.h>
 
 #include <algorithm>
 
@@ skipping 172 matching lines @@
 void OcclusionTracker::FinishedRenderTarget(
     const RenderSurfaceImpl* finished_target_surface) {
   // Make sure we know about the target surface.
   EnterRenderTarget(finished_target_surface);
 
   bool is_hidden =
       finished_target_surface->OwningEffectNode()->screen_space_opacity == 0.f;
 
   // Readbacks always happen on render targets so we only need to check
   // for readbacks here.
-  bool target_is_only_for_copy_request =
-      finished_target_surface->HasCopyRequest() && is_hidden;
+  bool target_is_only_for_copy_request_or_force_render_surface =
+      (finished_target_surface->HasCopyRequest() ||
+       finished_target_surface->ShouldCacheRenderSurface()) &&
+      is_hidden;
 
   // If the occlusion within the surface can not be applied to things outside of
   // the surface's subtree, then clear the occlusion here so it won't be used.
   if (finished_target_surface->HasMask() ||
       finished_target_surface->draw_opacity() < 1 ||
       !finished_target_surface->UsesDefaultBlendMode() ||
-      target_is_only_for_copy_request ||
+      target_is_only_for_copy_request_or_force_render_surface ||
       finished_target_surface->Filters().HasFilterThatAffectsOpacity()) {
     stack_.back().occlusion_from_outside_target.Clear();
     stack_.back().occlusion_from_inside_target.Clear();
   }
 }
 
 static void ReduceOcclusionBelowSurface(
     const RenderSurfaceImpl* contributing_surface,
     const gfx::Rect& surface_rect,
     const gfx::Transform& surface_transform,
@@ skipping 163 matching lines @@
   DCHECK(layer_tree->RootRenderSurface() == stack_.back().target);
   const SimpleEnclosedRegion& occluded =
       stack_.back().occlusion_from_inside_target;
   Region visible_region(screen_space_clip_rect_);
   for (size_t i = 0; i < occluded.GetRegionComplexity(); ++i)
     visible_region.Subtract(occluded.GetRect(i));
   return visible_region;
 }
 
 }  // namespace cc