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

Source/core/dom/AttrTest.cpp

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "config.h"
 #include "core/dom/Attr.h"
 
 #include "core/dom/Document.h"
 #include <gmock/gmock.h>
 #include <gtest/gtest.h>
 
-using namespace blink;
-
-namespace {
+namespace blink {
 
 class AttrTest : public ::testing::Test {
 protected:
-    virtual void SetUp() override;
+    void SetUp() override;
 
     PassRefPtrWillBeRawPtr<Attr> createAttribute();
     const AtomicString& value() const { return m_value; }
 
 private:
     RefPtrWillBePersistent<Document> m_document;
     AtomicString m_value;
 };
 
 void AttrTest::SetUp()
@@ skipping 46 matching lines @@
 }
 
 TEST_F(AttrTest, LengthOfContents)
 {
     RefPtrWillBeRawPtr<Attr> attr = createAttribute();
     EXPECT_EQ(0u, attr->lengthOfContents());
     attr->setValue(value());
     EXPECT_EQ(0u, attr->lengthOfContents());
 }
 
-} // unnamed namespace
+} // namespace blink