Make ui::Layer use the cc:LayerTreeHost scale factor directly

ui/compositor/compositor.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ui/compositor/compositor.h"
 
 #include <algorithm>
 #include <deque>
 
 #include "base/bind.h"
@@ skipping 256 matching lines @@
   DCHECK_GT(scale, 0);
   if (!size_in_pixel.IsEmpty()) {
     size_ = size_in_pixel;
     host_->SetViewportSize(size_in_pixel);
     root_web_layer_->SetBounds(size_in_pixel);
 
     next_draw_is_resize_ = true;
   }
   if (device_scale_factor_ != scale) {
     device_scale_factor_ = scale;
+    host_->SetDeviceScaleFactor(scale);
     if (root_layer_)
       root_layer_->OnDeviceScaleFactorChanged(scale);
   }
 }
 
 void Compositor::SetBackgroundColor(SkColor color) {
   host_->set_background_color(color);
   ScheduleDraw();
 }
 
@@ skipping 125 matching lines @@
     // CompositorObservers to be notified before starting another
     // draw cycle.
     ScheduleDraw();
   }
   FOR_EACH_OBSERVER(CompositorObserver,
                     observer_list_,
                     OnCompositingEnded(this));
 }
 
 }  // namespace ui