cc: Block drawing of tiles without twins.

cc/layers/picture_layer_impl.cc

Index: cc/layers/picture_layer_impl.cc
diff --git a/cc/layers/picture_layer_impl.cc b/cc/layers/picture_layer_impl.cc
index fb8f70150878e07eaa6e356d4301e0cba92caf19..0a60d61bab1a1789454b96fdcc2a0731c71cee0a 100644
--- a/cc/layers/picture_layer_impl.cc
+++ b/cc/layers/picture_layer_impl.cc
@@ -867,6 +867,13 @@ void PictureLayerImpl::MarkVisibleResourcesAsRequired() const {
       twin_high_res = high_res ? GetTwinTiling(high_res) : NULL;
     }
 
+    // When there is a race between activation+drawing and rasterizing,
+    // for tiles without twins, we should prevent the active tree from
+    // drawing these tiles.
+    if (twin_high_res && !twin_high_res->tiles_size()) {
+      layer_tree_impl()->SetRequiresHighResToDraw();

[sohanjg, 2014/09/08 13:45:16]

we should SetRequiresHighResToDraw, on the twin layer impl tree i think, but
that causes couple of tests *.NothingRequiredIfActiveMissingTiles fails, i am
checking them.

Also, will this be right place to block draw ?

+    }
+
     // If this layer and its twin have different transforms, then don't compare
     // them and only allow activating to high res tiles, since tiles on each
     // layer will be in different places on screen.