cc: Set requires high res upon becoming visible

cc/trees/layer_tree_host_impl.cc

Index: cc/trees/layer_tree_host_impl.cc
diff --git a/cc/trees/layer_tree_host_impl.cc b/cc/trees/layer_tree_host_impl.cc
index accd96710ca5a804983b6c100e2f16507bcccc28..f394d52494ea5750809c128277c1f25afb07d363 100644
--- a/cc/trees/layer_tree_host_impl.cc
+++ b/cc/trees/layer_tree_host_impl.cc
@@ -1737,10 +1737,12 @@ void LayerTreeHostImpl::SetVisible(bool visible) {
   DidVisibilityChange(this, visible_);
   EnforceManagedMemoryPolicy(ActualManagedMemoryPolicy());
 
-  if (!visible_) {
+  // If we just became visible, we have to ensure that we draw high res tiles,
+  // to prevent checkerboard/low res flashes.
+  if (visible_)
     active_tree()->SetRequiresHighResToDraw();

[enne (OOO), 2014/05/13 18:21:53]

I was originally going to suggest that maybe we set this flag on both trees when
not visible.

However, I think this is slightly better because it means we could have a fast
activation when not visible and there are no resources.  (Maybe we consider
auto-activating when not visible, honestly.)

[danakj, 2014/05/13 18:23:13]

Or when becoming visible. +1 to that either way.

+  else
     EvictAllUIResources();
-  }
 
   // Evict tiles immediately if invisible since this tab may never get another
   // draw or timer tick.