Cross-process frames should be notified of device scale factor changes.

content/renderer/render_widget.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 "content/renderer/render_widget.h"
 
 #include <memory>
 #include <utility>
 
 #include "base/auto_reset.h"
@@ skipping 1560 matching lines @@
 #else
   return !!webwidget_;
 #endif
 }
 
 void RenderWidget::SetDeviceScaleFactor(float device_scale_factor) {
   if (device_scale_factor_ == device_scale_factor)
     return;
 
   device_scale_factor_ = device_scale_factor;
+  // TODO(wjmaclean): do we need the following line? It only seems to matter for
+  // InitializeLayerTreeView, which only happens during initialization in which
+  // case the physical_backing_size is (I think) set via the view params set
+  // during construction.
+  physical_backing_size_ = gfx::ScaleToCeiledSize(size_, device_scale_factor_);
 
   OnDeviceScaleFactorChanged();
 
   ScheduleComposite();
 }
 
 bool RenderWidget::SetDeviceColorProfile(
     const std::vector<char>& color_profile) {
   if (device_color_profile_ == color_profile)
     return false;
@@ skipping 456 matching lines @@
 void RenderWidget::requestPointerUnlock() {
   mouse_lock_dispatcher_->UnlockMouse(webwidget_mouse_lock_target_.get());
 }
 
 bool RenderWidget::isPointerLocked() {
   return mouse_lock_dispatcher_->IsMouseLockedTo(
       webwidget_mouse_lock_target_.get());
 }
 
 }  // namespace content