core/platform: Include wtf files using "wtf/foo.h" form.

Source/core/platform/text/mac/StringImplMac.mm

 /*
  * Copyright (C) 2006, 2009 Apple Inc. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
  *
  * This library is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  * Library General Public License for more details.
  *
  * You should have received a copy of the GNU Library General Public License
  * along with this library; see the file COPYING.LIB.  If not, write to
  * the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
  * Boston, MA 02110-1301, USA.
  *
  */
 
 #include "config.h"
-#include <wtf/text/StringImpl.h>
+#include "wtf/text/StringImpl.h"
 
 #include "core/platform/mac/FoundationExtras.h"
-#include <wtf/RetainPtr.h>
+#include "wtf/RetainPtr.h"
 
 namespace WTF {
 
 StringImpl::operator NSString *()
 {
     return HardAutorelease(createCFString().leakRef());
 }
 
 }