Consolidate ShouldUseNativeFrame/AlwaysUseNativeFrame/UseNativeFrame spaghetti.

chrome/browser/external_tab_container_win.cc

Index: chrome/browser/external_tab_container_win.cc
===================================================================
--- chrome/browser/external_tab_container_win.cc	(revision 85647)
+++ chrome/browser/external_tab_container_win.cc	(working copy)
@@ -932,10 +932,14 @@
 }
 
 // ExternalTabContainer instances do not have a window.
-views::Window* ExternalTabContainer::GetWindow() {
+views::Window* ExternalTabContainer::GetContainingWindow() {
   return NULL;
 }
 
+const views::Window* ExternalTabContainer::GetContainingWindow() const {
+  return NULL;
+}
+
 bool ExternalTabContainer::AcceleratorPressed(
     const views::Accelerator& accelerator) {
   std::map<views::Accelerator, int>::const_iterator iter =