Part 1/3 (compositor) of adding with device scale factor to transport surfaces

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 8dec2f463b43ad57c89ee5f59b4c2e057c0ce799..b35425a9a77e81901eeca984e54007fc20f146a9 100644
--- a/cc/trees/layer_tree_host_impl.cc
+++ b/cc/trees/layer_tree_host_impl.cc
@@ -1205,6 +1205,10 @@ gfx::Size LayerTreeHostImpl::DeviceViewportSize() const {
   return device_viewport_size();
 }
 
+float LayerTreeHostImpl::DeviceScaleFactor() const {
+  return device_scale_factor_;
+}
+
 gfx::SizeF LayerTreeHostImpl::VisibleViewportSize() const {
   gfx::SizeF dip_size =
       gfx::ScaleSize(DeviceViewportSize(), 1.f / device_scale_factor());
@@ -1510,6 +1514,9 @@ void LayerTreeHostImpl::SetDeviceScaleFactor(float device_scale_factor) {
     return;
   device_scale_factor_ = device_scale_factor;
 
+  if (renderer_)
+    renderer_->ViewportChanged();
+
   UpdateMaxScrollOffset();
   SetFullRootLayerDamage();
 }