Be more specific about namespace for _ in unit tests

There is a gtest namespace ::testing and a helper namespace in blink
called ::blink::testing. If both are visible to the compiler,
::blink::testing will be used first and classes in ::testing will not
be found. This happens in jumbo builds so we better be more specific.

R=fs@opera.com

Change-Id: I4da27383432226191b0fcb72f3c54784698f0262
Reviewed-on: https://chromium-review.googlesource.com/574488Reviewed-by: Fredrik Söderquist <fs@opera.com>
Commit-Queue: Daniel Bratell <bratell@opera.com>
Cr-Commit-Position: refs/heads/master@{#487070}

third_party/WebKit/Source/core/dom/ScriptedIdleTaskControllerTest.cpp

@@ -120,7 +120,7 @@ TEST_F(ScriptedIdleTaskControllerTest, RunCallback) {
   EXPECT_TRUE(platform->HasIdleTask());
   EXPECT_NE(0, id);
 
-  EXPECT_CALL(*callback, handleEvent(testing::_));
+  EXPECT_CALL(*callback, handleEvent(::testing::_));
   platform->RunIdleTask();
   ::testing::Mock::VerifyAndClearExpectations(callback);
   EXPECT_FALSE(platform->HasIdleTask());
@@ -138,7 +138,7 @@ TEST_F(ScriptedIdleTaskControllerTest, DontRunCallbackWhenAskedToYield) {
   int id = controller->RegisterCallback(callback, options);
   EXPECT_NE(0, id);
 
-  EXPECT_CALL(*callback, handleEvent(testing::_)).Times(0);
+  EXPECT_CALL(*callback, handleEvent(::testing::_)).Times(0);
   platform->RunIdleTask();
   ::testing::Mock::VerifyAndClearExpectations(callback);