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

ios/web/test/web_test_suite.cc

Index: ios/web/test/web_test_suite.cc
diff --git a/ios/web/test/web_test_suite.cc b/ios/web/test/web_test_suite.cc
index cc218e9cc26d4791dfd4dcc761280c78ce86fb0e..ec72565024b87a8d2dc14b450f73acb198b1fbea 100644
--- a/ios/web/test/web_test_suite.cc
+++ b/ios/web/test/web_test_suite.cc
@@ -4,10 +4,24 @@
 
 #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) {
 }
@@ -22,6 +36,9 @@ void WebTestSuite::Initialize() {
   // 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