Make tile size a function of the device scale factor.

cc/trees/layer_tree_impl.cc

Index: cc/trees/layer_tree_impl.cc
diff --git a/cc/trees/layer_tree_impl.cc b/cc/trees/layer_tree_impl.cc
index c39359ae73e2cd33bd8fcf55b94150afc51c9069..2c58247354c691cfd529ba23780248c939dc47ab 100644
--- a/cc/trees/layer_tree_impl.cc
+++ b/cc/trees/layer_tree_impl.cc
@@ -1256,7 +1256,11 @@ gfx::Size LayerTreeImpl::DrawViewportSize() const {
   return layer_tree_host_impl_->DrawViewportSize();
 }
 
-const gfx::Rect LayerTreeImpl::ViewportRectForTilePriority() const {
+gfx::Size LayerTreeImpl::GetStableScreenSize() const {
+  return layer_tree_host_impl_->GetStableScreenSize(this);
+}
+
+gfx::Rect LayerTreeImpl::ViewportRectForTilePriority() const {
   return layer_tree_host_impl_->ViewportRectForTilePriority();
 }