Be explicit about namespace testing to not mix it with blink::testing

third_party/WebKit/Source/core/scheduler/ThrottlingTest.cpp

 // Copyright 2017 The Chromium Authors. All rights reserved.
 // Use of this source code if governed by a BSD-style license that can be
 // found in LICENSE file.
 
 #include "core/testing/sim/SimRequest.h"
 #include "core/testing/sim/SimTest.h"
 #include "platform/scheduler/child/web_scheduler.h"
 #include "platform/testing/RuntimeEnabledFeaturesTestHelpers.h"
 #include "platform/testing/UnitTestHelpers.h"
 #include "public/platform/Platform.h"
 #include "public/platform/WebThread.h"
 #include "public/platform/scheduler/renderer/renderer_scheduler.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
-using testing::ElementsAre;
+using ::testing::ElementsAre;
 
 namespace blink {
 
 class DisableBackgroundThrottlingIsRespectedTest : public SimTest {
  public:
   void SetUp() override {
     background_tab_timer_throttling_feature_ =
         WTF::MakeUnique<ScopedBackgroundTabTimerThrottlingForTest>(false);
     SimTest::SetUp();
   }
@@ skipping 66 matching lines @@
 
   // Make sure that we run a task once a second.
   for (int i = 0; i < 3; ++i) {
     testing::RunDelayedTasks(1000);
     EXPECT_THAT(ConsoleMessages(), ElementsAre("called f"));
     ConsoleMessages().clear();
   }
 }
 
 }  // namespace blink