Remove unused locks in mus ContextProvider classes

components/mus/public/cpp/lib/context_provider.cc

 // 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.
 
 #include "components/mus/public/cpp/context_provider.h"
 
 #include <stdint.h>
 
 #include "base/logging.h"
 #include "mojo/gles2/gles2_context.h"
@@ skipping 36 matching lines @@
   gpu::Capabilities capabilities;
   // Enabled the CHROMIUM_image extension to use GpuMemoryBuffers. The
   // implementation of which is used in CommandBufferDriver.
   capabilities.image = true;
   return capabilities;
 }
 
 void ContextProvider::SetupLock() {}
 
 base::Lock* ContextProvider::GetLock() {
-  return &context_lock_;
+  // This context provider is not used on multiple threads.
+  NOTREACHED();
+  return nullptr;
 }
 
 ContextProvider::~ContextProvider() {
   context_gl_.reset();
   if (context_)
     MojoGLES2DestroyContext(context_);
 }
 
 void ContextProvider::ContextLost() {}
 
 }  // namespace mus