[iOS] ios/web no longer depends on content::BrowserThread.

ios/web/test/web_test_suite.cc

 // Copyright 2013 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 "ios/web/test/web_test_suite.h"
 
+#include "base/macros.h"
 #include "base/metrics/statistics_recorder.h"
+#include "ios/web/web_thread_impl.h"
+#include "testing/gtest/include/gtest/gtest.h"
 
 namespace web {
 
+class WebTestSuiteListener : public testing::EmptyTestEventListener {
+ public:
+  WebTestSuiteListener() {}
+  void OnTestEnd(const testing::TestInfo& test_info) override {
+    WebThreadImpl::FlushThreadPoolHelperForTesting();
+  }
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(WebTestSuiteListener);
+};
+
 WebTestSuite::WebTestSuite(int argc, char** argv)
     : base::TestSuite(argc, argv) {
 }
 
 WebTestSuite::~WebTestSuite() {
 }
 
 void WebTestSuite::Initialize() {
   base::TestSuite::Initialize();
 
   // Initialize the histograms subsystem, so that any histograms hit in tests
   // are correctly registered with the statistics recorder and can be queried
   // by tests.
   base::StatisticsRecorder::Initialize();
+
+  testing::UnitTest::GetInstance()->listeners().Append(
+      new WebTestSuiteListener);
 }
 
 }  // namespace web