mus: Fix showing guest views in --mash and --mus.

content/browser/renderer_host/render_widget_host_view_aura.cc

Index: content/browser/renderer_host/render_widget_host_view_aura.cc
diff --git a/content/browser/renderer_host/render_widget_host_view_aura.cc b/content/browser/renderer_host/render_widget_host_view_aura.cc
index 2c8d5b5dc6946e01eb5aab819bab4949a2da6b09..16ba949b17734503adb2d66192b0edb2fbe1f7e8 100644
--- a/content/browser/renderer_host/render_widget_host_view_aura.cc
+++ b/content/browser/renderer_host/render_widget_host_view_aura.cc
@@ -1585,6 +1585,13 @@ bool RenderWidgetHostViewAura::HasHitTestMask() const {
 void RenderWidgetHostViewAura::GetHitTestMask(gfx::Path* mask) const {
 }
 
+void RenderWidgetHostViewAura::OnWindowSurfaceChanged(
+    const cc::SurfaceInfo& surface_info) {
+  if (!is_guest_view_hack_)
+    return;
+  host_->GetView()->OnSurfaceChanged(surface_info);
+}
+
 ////////////////////////////////////////////////////////////////////////////////
 // RenderWidgetHostViewAura, ui::EventHandler implementation: