Plumb physical backing size from RWHV to renderer CC.

content/renderer/render_widget.cc

Index: content/renderer/render_widget.cc
diff --git a/content/renderer/render_widget.cc b/content/renderer/render_widget.cc
index d4c3ac0cfd952ec8df8051347de27672e1e6dfd4..fa1900addeabd7fdbf3dff7e3f98b23ca07604dd 100644
--- a/content/renderer/render_widget.cc
+++ b/content/renderer/render_widget.cc
@@ -329,6 +329,7 @@ bool RenderWidget::Send(IPC::Message* message) {
 }
 
 void RenderWidget::Resize(const gfx::Size& new_size,
+                          const gfx::Size& physical_backing_size,
                           const gfx::Rect& resizer_rect,
                           bool is_fullscreen,
                           ResizeAck resize_ack) {
@@ -340,7 +341,10 @@ void RenderWidget::Resize(const gfx::Size& new_size,
   if (!webwidget_)
     return;
 
-  // Remember the rect where the resize corner will be drawn.
+  if (compositor_)
+    compositor_->setViewportSize(new_size, physical_backing_size);
+
+  physical_backing_size_ = physical_backing_size_;
   resizer_rect_ = resizer_rect;
 
   // NOTE: We may have entered fullscreen mode without changing our size.
@@ -414,9 +418,11 @@ void RenderWidget::OnCreatingNewAck() {
 }
 
 void RenderWidget::OnResize(const gfx::Size& new_size,
+                            const gfx::Size& physical_backing_size,
                             const gfx::Rect& resizer_rect,
                             bool is_fullscreen) {
-  Resize(new_size, resizer_rect, is_fullscreen, SEND_RESIZE_ACK);
+  Resize(new_size, physical_backing_size, resizer_rect, is_fullscreen,
+         SEND_RESIZE_ACK);
 }
 
 void RenderWidget::OnChangeResizeRect(const gfx::Rect& resizer_rect) {
@@ -1347,6 +1353,7 @@ void RenderWidget::initializeLayerTreeView(
     return;
 
   compositor_->setRootLayer(root_layer);
+  compositor_->setViewportSize(size_, physical_backing_size_);
   if (init_complete_)
     compositor_->setSurfaceReady();
 }