gfx: Make conversions from Size to SizeF be explicit.

cc/test/layer_tree_test.cc

Index: cc/test/layer_tree_test.cc
diff --git a/cc/test/layer_tree_test.cc b/cc/test/layer_tree_test.cc
index c87c36b780ba0f07a8008cf00a459ca8e131013d..ccf1dbee46f699dd1f743d384b7a3637d64e1cb6 100644
--- a/cc/test/layer_tree_test.cc
+++ b/cc/test/layer_tree_test.cc
@@ -803,8 +803,8 @@ void LayerTreeTest::SetupTree() {
   }
 
   gfx::Size root_bounds = layer_tree_host_->root_layer()->bounds();
-  gfx::Size device_root_bounds = gfx::ToCeiledSize(
-      gfx::ScaleSize(root_bounds, layer_tree_host_->device_scale_factor()));
+  gfx::Size device_root_bounds = gfx::ScaleToCeiledSize(
+      root_bounds, layer_tree_host_->device_scale_factor());
   layer_tree_host_->SetViewportSize(device_root_bounds);
 }