Makes copying layers clone external textures.

ui/views/widget/desktop_native_widget_aura.cc

Index: ui/views/widget/desktop_native_widget_aura.cc
diff --git a/ui/views/widget/desktop_native_widget_aura.cc b/ui/views/widget/desktop_native_widget_aura.cc
index 56f972b4b03814509272f4f23e6bc88b0045eb70..ea5d64465d5345a950314c9c674c69dfc9da8521 100644
--- a/ui/views/widget/desktop_native_widget_aura.cc
+++ b/ui/views/widget/desktop_native_widget_aura.cc
@@ -369,6 +369,13 @@ bool DesktopNativeWidgetAura::HasHitTestMask() const {
 void DesktopNativeWidgetAura::GetHitTestMask(gfx::Path* mask) const {
 }
 
+scoped_refptr<ui::Texture> DesktopNativeWidgetAura::CopyTexture() {
+  // The layer we create doesn't have an external texture, so this should never
+  // get invoked.
+  NOTREACHED();
+  return scoped_refptr<ui::Texture>();
+}
+
 ////////////////////////////////////////////////////////////////////////////////
 // DesktopNativeWidgetAura, ui::EventHandler implementation: