Plumb physical backing size from RWHV to renderer CC.

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 85108c053db54eb8daea217da1176964d6d4d462..daba667757bc0b06966c7747ee1da73842a9dc54 100644
--- a/content/browser/renderer_host/render_widget_host_impl.cc
+++ b/content/browser/renderer_host/render_widget_host_impl.cc
@@ -481,26 +481,30 @@ void RenderWidgetHostImpl::WasResized() {
   gfx::Rect view_bounds = view_->GetViewBounds();
   gfx::Size new_size(view_bounds.size());
 
+  gfx::Size old_physical_backing_size = physical_backing_size_;
+  physical_backing_size_ = view_->GetPhysicalBackingSize();
   bool was_fullscreen = is_fullscreen_;
   is_fullscreen_ = IsFullscreen();
-  bool fullscreen_changed = was_fullscreen != is_fullscreen_;
+
   bool size_changed = new_size != current_size_;
+  bool side_payload_changed =
+      old_physical_backing_size != physical_backing_size_ ||
+      was_fullscreen != is_fullscreen_;
 
-  // Avoid asking the RenderWidget to resize to its current size, since it
-  // won't send us a PaintRect message in that case.
-  if (!size_changed && !fullscreen_changed)
+  if (!size_changed && !side_payload_changed)
     return;
 
   if (in_flight_size_ != gfx::Size() && new_size == in_flight_size_ &&
-      !fullscreen_changed)
+      !side_payload_changed)
     return;
 
-  // We don't expect to receive an ACK when the requested size is empty.
+  // We don't expect to receive an ACK when the requested size is empty or when
+  // the main viewport size didn't change.
   if (!new_size.IsEmpty() && size_changed)
     resize_ack_pending_ = true;
 
-  if (!Send(new ViewMsg_Resize(routing_id_, new_size,
-          GetRootWindowResizerRect(), is_fullscreen_))) {
+  if (!Send(new ViewMsg_Resize(routing_id_, new_size, physical_backing_size_,
+                               GetRootWindowResizerRect(), is_fullscreen_))) {
     resize_ack_pending_ = false;
   } else {
     in_flight_size_ = new_size;