compositor worker: Use a WebThread for the compositor thread.

components/scheduler/child/webthread_impl_for_worker_scheduler_unittest.cc

 // Copyright 2015 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/scheduler/child/webthread_impl_for_worker_scheduler.h"
 
 #include "base/macros.h"
 #include "base/synchronization/waitable_event.h"
 #include "components/scheduler/child/web_scheduler_impl.h"
 #include "components/scheduler/child/worker_scheduler_impl.h"
@@ skipping 75 matching lines @@
 }  // namespace
 
 class WebThreadImplForWorkerSchedulerTest : public testing::Test {
  public:
   WebThreadImplForWorkerSchedulerTest() {}
 
   ~WebThreadImplForWorkerSchedulerTest() override {}
 
   void SetUp() override {
     thread_.reset(new WebThreadImplForWorkerScheduler("test thread"));
+    thread_->Init();
   }
 
   void RunOnWorkerThread(const tracked_objects::Location& from_here,
                          const base::Closure& task) {
     base::WaitableEvent completion(false, false);
     thread_->TaskRunner()->PostTask(
         from_here,
         base::Bind(&WebThreadImplForWorkerSchedulerTest::RunOnWorkerThreadTask,
                    base::Unretained(this), task, &completion));
     completion.Wait();
@@ skipping 79 matching lines @@
   EXPECT_CALL(*delayed_task, run()).Times(0);
 
   RunOnWorkerThread(FROM_HERE, base::Bind(&shutdownOnThread, thread_.get()));
   thread_->taskRunner()->postTask(blink::WebTraceLocation(), task.release());
   thread_->taskRunner()->postDelayedTask(blink::WebTraceLocation(),
                                          task.release(), 50ll);
   thread_.reset();
 }
 
 }  // namespace scheduler