Work on separate browser contexts

ui/gfx/screen.cc

 // Copyright 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "base/logging.h"
 #include "ui/gfx/screen.h"
 #include "ui/gfx/screen_type_delegate.h"
 
 namespace gfx {
 
@@ skipping 17 matching lines @@
     type = g_screen_type_delegate_->GetScreenTypeForNativeView(view);
   if (type == SCREEN_TYPE_NATIVE)
     return GetNativeScreen();
   DCHECK(g_screen_[type]);
   return g_screen_[type];
 }
 
 // static
 void Screen::SetScreenInstance(ScreenType type, Screen* instance) {
   DCHECK_LE(type, SCREEN_TYPE_LAST);
+  DCHECK(!g_screen_[type]);
   g_screen_[type] = instance;
 }
 
 // static
+Screen* Screen::GetScreenByType(ScreenType type) {
+  DCHECK(g_screen_[type]);
+  return g_screen_[type];
+}
+
+// static
 void Screen::SetScreenTypeDelegate(ScreenTypeDelegate* delegate) {
   g_screen_type_delegate_ = delegate;
 }
 
 // static
 Screen* Screen::GetNativeScreen() {
   if (!g_screen_[SCREEN_TYPE_NATIVE])
     g_screen_[SCREEN_TYPE_NATIVE] = CreateNativeScreen();
   return g_screen_[SCREEN_TYPE_NATIVE];
 }
 
 }  // namespace gfx