Don't clear render surfaces unnecessarily.

cc/trees/layer_tree_host_common.h

Index: cc/trees/layer_tree_host_common.h
diff --git a/cc/trees/layer_tree_host_common.h b/cc/trees/layer_tree_host_common.h
index 20b2163da11f1845d3f6a0a968a26e918d1d9a0a..ba5d579a5de7ec9a3ca178f434abc71b7621c951 100644
--- a/cc/trees/layer_tree_host_common.h
+++ b/cc/trees/layer_tree_host_common.h
@@ -139,6 +139,11 @@ class CC_EXPORT LayerTreeHostCommon {
     return children[index];
   }
 
+  static LayerImpl* get_child_as_raw_ptr(const LayerImplList& children,

[danakj, 2014/04/25 22:59:24]

Would you mind doing a followup CL to rename all three of these methods to not
refer to children?

[Ian Vollick, 2014/04/25 23:14:39]

Totally.

+                                         size_t index) {
+    return children[index];
+  }
+
   struct ScrollUpdateInfo {
     int layer_id;
     gfx::Vector2d scroll_delta;