Change all platforms except Windows to access the clipboard solely from the UI thread

ui/base/clipboard/clipboard.h

 // Copyright (c) 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.
 
 #ifndef UI_BASE_CLIPBOARD_CLIPBOARD_H_
 #define UI_BASE_CLIPBOARD_CLIPBOARD_H_
 #pragma once
 
 #include <map>
 #include <string>
 #include <vector>
 
+#include "base/compiler_specific.h"
 #include "base/gtest_prod_util.h"
 #include "base/process.h"
 #include "base/shared_memory.h"
 #include "base/string16.h"
+#include "base/threading/thread_checker.h"
 #include "ui/base/ui_export.h"
 
 #if defined(TOOLKIT_USES_GTK)
 #include <gdk/gdk.h>
 #endif
 
 #if defined(OS_ANDROID)
 #include <jni.h>
 
 #include "base/android/jni_android.h"
@@ skipping 12 matching lines @@
 #endif
 
 #ifdef __OBJC__
 @class NSString;
 #else
 class NSString;
 #endif
 
 namespace ui {
 
-class UI_EXPORT Clipboard {
+class UI_EXPORT Clipboard : NON_EXPORTED_BASE(public base::ThreadChecker) {
  public:
   // MIME type constants.
   static const char kMimeTypeText[];
   static const char kMimeTypeURIList[];
   static const char kMimeTypeDownloadURL[];
   static const char kMimeTypeHTML[];
   static const char kMimeTypePNG[];
 
   // Platform neutral holder for native data representation of a clipboard type.
   struct UI_EXPORT FormatType {
@@ skipping 299 matching lines @@
   jmethodID get_text_;
   jmethodID to_string_;
 #endif
 
   DISALLOW_COPY_AND_ASSIGN(Clipboard);
 };
 
 }  // namespace ui
 
 #endif  // UI_BASE_CLIPBOARD_CLIPBOARD_H_