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 1550 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_);

[oshima, 2016/07/12 14:14:41]

physical_backing_size_ is resized in OnResize.

I think it's better to fold this method into OnResize, and then rename this to
OnSetDeviceScaleFactor. Update the size after OnDeviceScaleFactorChanged to keep
the order in sync with OnResize.

[wjmaclean, 2016/07/29 17:12:37]

I'm not sure I follow. By "fold" do you mean to put the code above this comment
into OnResize()?

When you say "update the size" do you mean the value of physical_backing _size_?
We cannot call OnResize() from here since we only have a new device scale
factor, and not an entire set of resize params. Finally, if we rename this to
OnSetDeviceScaleFactor, is that what the other current callers of this function
should call? If so, the logic they were expecting won't be here anymore.

[oshima, 2016/07/29 18:11:46]

Yes.
What I meant is to update & call stuff in the same order as OnResize.
It looks to me that OnResize is the only caller. Am I wrong?

 
   OnDeviceScaleFactorChanged();
 
   ScheduleComposite();
 }
 
 bool RenderWidget::SetDeviceColorProfile(
     const std::vector<char>& color_profile) {
   if (device_color_profile_ == color_profile)
     return false;
@@ skipping 398 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