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

content/browser/renderer_host/render_widget_host_impl.cc

Index: content/browser/renderer_host/render_widget_host_impl.cc
diff --git a/content/browser/renderer_host/render_widget_host_impl.cc b/content/browser/renderer_host/render_widget_host_impl.cc
index 8c8bae4d2a923c28f62218a6a14ad6ca02fd40e5..280123ea75839293f9958ec6a662d91a58dd565d 100644
--- a/content/browser/renderer_host/render_widget_host_impl.cc
+++ b/content/browser/renderer_host/render_widget_host_impl.cc
@@ -588,6 +588,9 @@ bool RenderWidgetHostImpl::GetResizeParams(ResizeParams* resize_params) {
 
   if (view_) {
     resize_params->new_size = view_->GetRequestedRendererSize();
+    // TODO(wjmaclean): Can we just get rid of physical_backing_size and just
+    // deal with it on the renderer side? It seems to always be
+    // ScaleToCeiledSize(new_size, device_scale_factor) ??
     resize_params->physical_backing_size = view_->GetPhysicalBackingSize();
     resize_params->top_controls_height = view_->GetTopControlsHeight();
     resize_params->top_controls_shrink_blink_size =
@@ -1214,10 +1217,13 @@ void RenderWidgetHostImpl::RemoveInputEventObserver(
 
 void RenderWidgetHostImpl::GetWebScreenInfo(blink::WebScreenInfo* result) {
   TRACE_EVENT0("renderer_host", "RenderWidgetHostImpl::GetWebScreenInfo");
-  if (view_)
+  if (view_) {
     view_->GetScreenInfo(result);
-  else
+  } else {
     RenderWidgetHostViewBase::GetDefaultScreenInfo(result);
+    // The delegate may have more up-to-date information if we're a sub-frame.
+    result->deviceScaleFactor = delegate_->DefaultDeviceScaleFactor();

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

Since delegate_ is always available (except for shutdown), it probably makes
sense to implement

delegate_->GetScreenInfo(WebScreenInfo*)

instead, and let WebContentsImpl ask WebContentsView to get the WebScreenInfo,
instead of RWHV. You should be able to move the GetScerenInfo impl from RWHV
impl to WebContentsView impl.

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

Done (I think).

I've moved the GetScreenInfo() machinery into the WebContentsView* hierarchy ...
it involved moving a lot of stuff around, so please let me know if what I've
done matches what you had in mind.

+  }
   // TODO(sievers): find a way to make this done another way so the method
   // can be const.
   latency_tracker_.set_device_scale_factor(result->deviceScaleFactor);