(not for review yet)

cc/trees/layer_tree_impl.h

Index: cc/trees/layer_tree_impl.h
diff --git a/cc/trees/layer_tree_impl.h b/cc/trees/layer_tree_impl.h
index 4dfc51110520c23755ce58e142d3b5ec135e4cd9..d2f69c12d4fe23e295dc433c8772a9cc2c04d71c 100644
--- a/cc/trees/layer_tree_impl.h
+++ b/cc/trees/layer_tree_impl.h
@@ -179,6 +179,11 @@ class CC_EXPORT LayerTreeImpl {
 
   void DidBecomeActive();
 
+  void SetUIResourceEvictionCountAcked(uint64 ui_resource_eviction_count_acked);
+  uint64 ui_resource_eviction_count_acked() const {
+    return ui_resource_eviction_count_acked_;
+  }
+
   bool ContentsTexturesPurged() const;
   void SetContentsTexturesPurged();
   void ResetContentsTexturesPurged();
@@ -243,6 +248,12 @@ class CC_EXPORT LayerTreeImpl {
   // rendering and input event hit testing.
   LayerImplList render_surface_layer_list_;
 
+  // The UI resource eviction count most recently acked. This value is updated
+  // through ProcessUIResourceRequestQueue. If this value is not equal to
+  // |layer_tree_host_impl_|'s UI resource eviction count, then this tree may
+  // may reference evicted UI resources and cannot be drawn.
+  uint64 ui_resource_eviction_count_acked_;
+
   bool contents_textures_purged_;
   bool viewport_size_invalid_;
   bool needs_update_draw_properties_;