Correctly set up the context lock in ui::InProcessContextProvider

ContextCacheController needs the context lock, but was not set up in
ui::InProcessContextProvider, causing data races.

Bug: 845173
Change-Id: Ia9e3ae509efd2aa880f80fde55d92bd835db32b9
Reviewed-on: https://chromium-review.googlesource.com/1067537Reviewed-by: Victor Miura <vmiura@chromium.org>
Commit-Queue: Antoine Labour <piman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#560358}

ui/compositor/test/in_process_context_provider.cc

@@ -109,6 +109,8 @@ gpu::ContextResult InProcessContextProvider::BindToCurrentThread() {
 
   cache_controller_ = std::make_unique<viz::ContextCacheController>(
       context_->GetImplementation(), base::ThreadTaskRunnerHandle::Get());
+  if (support_locking_)
+    cache_controller_->SetLock(GetLock());
 
   std::string unique_context_name =
       base::StringPrintf("%s-%p", debug_name_.c_str(), context_.get());