Fix unit test style in core/{dom,editing,html}/.

Source/core/dom/MainThreadTaskRunnerTest.cpp

Index: Source/core/dom/MainThreadTaskRunnerTest.cpp
diff --git a/Source/core/dom/MainThreadTaskRunnerTest.cpp b/Source/core/dom/MainThreadTaskRunnerTest.cpp
index 1ad4b872dfacf9a3311ef63f57375ff8662aa436..cb1d63da9f02301a02a389592ba630e031d1fc43 100644
--- a/Source/core/dom/MainThreadTaskRunnerTest.cpp
+++ b/Source/core/dom/MainThreadTaskRunnerTest.cpp
@@ -37,9 +37,7 @@
 #include "wtf/PassOwnPtr.h"
 #include <gtest/gtest.h>
 
-using namespace blink;
-
-namespace {
+namespace blink {
 
 class MarkingBooleanTask final : public ExecutionContextTask {
 public:
@@ -105,4 +103,4 @@ TEST(MainThreadTaskRunnerTest, RemoveRunner)
     EXPECT_FALSE(isMarked);
 }
 
-}
+} // namespace blink