Remove unused locks in mus ContextProvider classes

components/mus/surfaces/surfaces_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/surfaces/surfaces_context_provider.h"
 
 #include <stddef.h>
 
 #include "base/bind.h"
 #include "base/bind_helpers.h"
@@ skipping 75 matching lines @@
 
 void SurfacesContextProvider::InvalidateGrContext(uint32_t state) {}
 
 gpu::Capabilities SurfacesContextProvider::ContextCapabilities() {
   return capabilities_;
 }
 
 void SurfacesContextProvider::SetupLock() {}
 
 base::Lock* SurfacesContextProvider::GetLock() {
-  return &context_lock_;
+  // This context provider is not used on multiple threads.
+  NOTREACHED();
+  return nullptr;
 }
 
 void SurfacesContextProvider::SetLostContextCallback(
     const LostContextCallback& lost_context_callback) {
   implementation_->SetLostContextCallback(lost_context_callback);
 }
 
 SurfacesContextProvider::~SurfacesContextProvider() {
   implementation_->Flush();
   implementation_.reset();
@@ skipping 14 matching lines @@
     swap_buffers_completion_callback_.Run(result);
   }
 }
 
 void SurfacesContextProvider::SetSwapBuffersCompletionCallback(
     gfx::GLSurface::SwapCompletionCallback callback) {
   swap_buffers_completion_callback_ = callback;
 }
 
 }  // namespace mus