Remove unused locks in mus ContextProvider classes

components/mus/public/cpp/context_provider.h

 // Copyright 2014 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 COMPONENTS_MUS_PUBLIC_CPP_CONTEXT_PROVIDER_H_
 #define COMPONENTS_MUS_PUBLIC_CPP_CONTEXT_PROVIDER_H_
 
 #include <stdint.h>
 
 #include <memory>
 
 #include "base/macros.h"
-#include "base/synchronization/lock.h"
 #include "cc/output/context_provider.h"
 #include "mojo/public/c/gles2/gles2_types.h"
 #include "mojo/public/cpp/system/core.h"
 
 namespace mus {
 
 class ContextProvider : public cc::ContextProvider {
  public:
   explicit ContextProvider(mojo::ScopedMessagePipeHandle command_buffer_handle);
 
@@ skipping 17 matching lines @@
  private:
   static void ContextLostThunk(void* closure) {
     static_cast<ContextProvider*>(closure)->ContextLost();
   }
   void ContextLost();
 
   mojo::ScopedMessagePipeHandle command_buffer_handle_;
   MojoGLES2Context context_;
   std::unique_ptr<gpu::gles2::GLES2Interface> context_gl_;
 
-  base::Lock context_lock_;
-
   DISALLOW_COPY_AND_ASSIGN(ContextProvider);
 };
 
 }  // namespace mus
 
 #endif  // COMPONENTS_MUS_PUBLIC_CPP_CONTEXT_PROVIDER_H_