Implement ui::ClipboardMus.

base/threading/thread_restrictions.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 BASE_THREADING_THREAD_RESTRICTIONS_H_
 #define BASE_THREADING_THREAD_RESTRICTIONS_H_
 
 #include "base/base_export.h"
 #include "base/macros.h"
 
@@ skipping 64 matching lines @@
 
 namespace remoting {
 class AutoThread;
 }
 
 namespace ui {
 class WindowResizeHelperMac;
 }
 
 namespace views {
+class ClipboardMus;
 class ScreenMus;
 }
 
 namespace base {
 
 namespace android {
 class JavaHandlerThread;
 }
 
 class SequencedWorkerPool;
@@ skipping 133 matching lines @@
   friend class disk_cache::BackendImpl;           // http://crbug.com/74623
   friend class disk_cache::InFlightIO;            // http://crbug.com/74623
   friend class gpu::GpuChannelHost;               // http://crbug.com/125264
   friend class net::internal::AddressTrackerLinux;  // http://crbug.com/125097
   friend class net::NetworkChangeNotifierMac;     // http://crbug.com/125097
   friend class ::BrowserProcessImpl;              // http://crbug.com/125207
   friend class ::NativeBackendKWallet;            // http://crbug.com/125331
 #if !defined(OFFICIAL_BUILD)
   friend class content::SoftwareOutputDeviceMus;  // Interim non-production code
 #endif
+  friend class views::ClipboardMus;

[brettw, 2016/06/03 21:39:00]

I think it would be good to have a comment here about why this must be blocking
(like your review comment).

   friend class views::ScreenMus;
 // END USAGE THAT NEEDS TO BE FIXED.
 
 #if ENABLE_THREAD_RESTRICTIONS
   static bool SetWaitAllowed(bool allowed);
 #else
   static bool SetWaitAllowed(bool allowed) { return true; }
 #endif
 
   // Constructing a ScopedAllowWait temporarily allows waiting on the current
@@ skipping 11 matching lines @@
 
     DISALLOW_COPY_AND_ASSIGN(ScopedAllowWait);
   };
 
   DISALLOW_IMPLICIT_CONSTRUCTORS(ThreadRestrictions);
 };
 
 }  // namespace base
 
 #endif  // BASE_THREADING_THREAD_RESTRICTIONS_H_