clang/blink_gc_plugin: Replace 'WebCore' with 'blink'

tools/clang/blink_gc_plugin/tests/ignore_class.cpp

 // Copyright 2014 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 "ignore_class.h"
 
-namespace WebCore {
+namespace blink {
 
 void B::trace(Visitor* visitor)
 {
     // Class is ignored so no checking here.
 }
 
 void C::trace(Visitor* visitor)
 {
     // Missing trace of m_obj.
     // Ignored base class B does not need tracing.
 }
 
 }