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

There are two namespaces named testing used in Blink unit tests, one
from gtest and one internal helper namespace. If both are visible then
the gtest testing namespace won't be used unless prepended with ::, as
is already done in large parts of the code.

BUG=739121
R=haraken@opera.com

Change-Id: I48f6a3145886253576a53d1ad9c08307ceca0d52
Reviewed-on: https://chromium-review.googlesource.com/567143Reviewed-by: Kentaro Hara <haraken@chromium.org>
Commit-Queue: Daniel Bratell <bratell@opera.com>
Cr-Commit-Position: refs/heads/master@{#486839}

third_party/WebKit/Source/platform/image-decoders/ImageDecoderTest.cpp

@@ -239,7 +239,7 @@ TEST(ImageDecoderTest, clearCacheExceptFrameAll) {
   decoder->ClearCacheExceptFrame(kNotFound);
 
   for (size_t i = 0; i < kNumFrames; ++i) {
-    SCOPED_TRACE(testing::Message() << i);
+    SCOPED_TRACE(::testing::Message() << i);
     EXPECT_EQ(ImageFrame::kFrameEmpty, frame_buffers[i].GetStatus());
   }
 }
@@ -256,7 +256,7 @@ TEST(ImageDecoderTest, clearCacheExceptFramePreverveClearExceptFrame) {
   decoder->ResetRequiredPreviousFrames();
   decoder->ClearCacheExceptFrame(5);
   for (size_t i = 0; i < kNumFrames; ++i) {
-    SCOPED_TRACE(testing::Message() << i);
+    SCOPED_TRACE(::testing::Message() << i);
     if (i == 5)
       EXPECT_EQ(ImageFrame::kFrameComplete, frame_buffers[i].GetStatus());
     else

third_party/WebKit/Source/platform/scheduler/base/task_queue_selector_unittest.cc

@@ -220,10 +220,10 @@ TEST_F(TaskQueueSelectorTest, TestDisableEnable) {
   selector_.EnableQueue(task_queues_[2].get());
   selector_.SetQueuePriority(task_queues_[2].get(),
                              TaskQueue::BEST_EFFORT_PRIORITY);
-  EXPECT_THAT(PopTasks(), testing::ElementsAre(2));
+  EXPECT_THAT(PopTasks(), ::testing::ElementsAre(2));
   task_queues_[4]->SetQueueEnabledForTest(true);
   selector_.EnableQueue(task_queues_[4].get());
-  EXPECT_THAT(PopTasks(), testing::ElementsAre(4));
+  EXPECT_THAT(PopTasks(), ::testing::ElementsAre(4));
 }
 
 TEST_F(TaskQueueSelectorTest, TestDisableChangePriorityThenEnable) {