cc: Use ScreenSpaceTransform to determine content scale

cc/test/layer_tree_host_common_test.cc

Index: cc/test/layer_tree_host_common_test.cc
diff --git a/cc/test/layer_tree_host_common_test.cc b/cc/test/layer_tree_host_common_test.cc
index a064bbca16c159973d3c0a8751082b18ae0d9350..16a2597f47ec39d21890b6528708514eaea4aa66 100644
--- a/cc/test/layer_tree_host_common_test.cc
+++ b/cc/test/layer_tree_host_common_test.cc
@@ -178,6 +178,8 @@ void LayerTreeHostCommonTestBase::ExecuteCalculateDrawProperties(
     bool layers_always_allowed_lcd_text) {
   root_layer->layer_tree_impl()->SetDeviceScaleFactor(device_scale_factor);
 
+  EXPECT_TRUE(page_scale_layer || (page_scale_factor == 1.f));
+
   gfx::Transform identity_matrix;
   gfx::Size device_viewport_size =
       gfx::Size(root_layer->bounds().width() * device_scale_factor,