cc: don't add low-res tiling to GPU rasterized layers.

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 08b42c5f63a7d6d690033e9a99390f6810a7bf24..8765af1537cc0b02ecc31164c19fc507054e23f9 100644
--- a/cc/layers/picture_layer_impl.cc
+++ b/cc/layers/picture_layer_impl.cc
@@ -945,8 +945,9 @@ void PictureLayerImpl::ManageTilings(bool animating_transform_to_screen) {
   // prevents wastefully creating a paired low res tiling for every new high res
   // tiling during a pinch or a CSS animation.
   bool is_pinching = layer_tree_impl()->PinchGestureActive();
-  if (!is_pinching && !animating_transform_to_screen && !low_res &&
-      low_res != high_res)
+  if (ShouldHaveLowResTiling() && !is_pinching &&
+      !animating_transform_to_screen &&
+      !low_res && low_res != high_res)
     low_res = AddTiling(low_res_raster_contents_scale_);
 
   // Set low-res if we have one.
@@ -1093,7 +1094,7 @@ void PictureLayerImpl::CleanUpTilingsOnActiveLayer(
       continue;
 
     // Low resolution can't activate, so only keep one around.

[ernstm, 2014/01/10 17:37:43]

Is this comment not up to date? It looks like we were keeping all low-res
tilings before my change.

[enne (OOO), 2014/01/10 17:48:57]

We can activate to low res now.  I think the comment is just wrong.

[ernstm, 2014/01/10 17:53:32]

I updated the comment.

-    if (tiling->resolution() == LOW_RESOLUTION)
+    if (tiling->resolution() == LOW_RESOLUTION && ShouldHaveLowResTiling())

[ernstm, 2014/01/10 17:37:43]

This should work, right?

[enne (OOO), 2014/01/10 17:48:57]

Yup.

       continue;
 
     // Don't remove tilings that are being used (and thus would cause a flash.)