cc: Fix a hang in image controller unittests by release task lock.

cc/tiles/image_controller_unittest.cc

 // Copyright 2016 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 "base/bind.h"
 #include "base/optional.h"
 #include "base/run_loop.h"
 #include "base/test/test_simple_task_runner.h"
 #include "base/threading/sequenced_task_runner_handle.h"
 #include "cc/tiles/image_controller.h"
 #include "cc/tiles/image_decode_cache.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
 namespace cc {
 namespace {
 
 class TestWorkerThread : public base::SimpleThread {
  public:
   TestWorkerThread()
       : base::SimpleThread("test_worker_thread"), condition_(&lock_) {}
 
   void Run() override {
     for (;;) {
-      base::AutoLock hold(lock_);
-      if (shutdown_)
-        break;
+      base::Closure task;
+      {
+        base::AutoLock hold(lock_);
+        if (shutdown_)
+          break;
 
-      if (queue_.empty()) {
-        condition_.Wait();
-        continue;
+        if (queue_.empty()) {
+          condition_.Wait();
+          continue;
+        }
+
+        task = queue_.front();
+        queue_.erase(queue_.begin());
       }
-
-      queue_.front().Run();
-      queue_.erase(queue_.begin());
+      task.Run();
     }
   }
 
   void Shutdown() {
     base::AutoLock hold(lock_);
     shutdown_ = true;
     condition_.Signal();
   }
 
   void PostTask(const base::Closure& task) {
@@ skipping 393 matching lines @@
   EXPECT_EQ(expected_id1, decode_client1.id());
   EXPECT_TRUE(task->has_run());
   EXPECT_EQ(1, cache()->number_of_refs());
 
   controller()->SetImageDecodeCache(nullptr);
   EXPECT_EQ(0, cache()->number_of_refs());
 }
 
 }  // namespace
 }  // namespace cc