Update {virtual,override} to follow C++11 style in tools.

tools/clang/blink_gc_plugin/Edge.h

 // 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.
 
 #ifndef TOOLS_BLINK_GC_PLUGIN_EDGE_H_
 #define TOOLS_BLINK_GC_PLUGIN_EDGE_H_
 
 #include <deque>
 
 #include "TracingStatus.h"
@@ skipping 21 matching lines @@
   virtual void VisitMember(Member*) {}
   virtual void VisitWeakMember(WeakMember*) {}
   virtual void VisitPersistent(Persistent*) {}
   virtual void VisitCollection(Collection*) {}
 };
 
 // Recursive edge visitor. The traversed path is accessible in context.
 class RecursiveEdgeVisitor : public EdgeVisitor {
  public:
   // Overrides that recursively walk the edges and record the path.
-  virtual void VisitValue(Value*) override;
-  virtual void VisitRawPtr(RawPtr*) override;
-  virtual void VisitRefPtr(RefPtr*) override;
-  virtual void VisitOwnPtr(OwnPtr*) override;
-  virtual void VisitMember(Member*) override;
-  virtual void VisitWeakMember(WeakMember*) override;
-  virtual void VisitPersistent(Persistent*) override;
-  virtual void VisitCollection(Collection*) override;
+  void VisitValue(Value*) override;
+  void VisitRawPtr(RawPtr*) override;
+  void VisitRefPtr(RefPtr*) override;
+  void VisitOwnPtr(OwnPtr*) override;
+  void VisitMember(Member*) override;
+  void VisitWeakMember(WeakMember*) override;
+  void VisitPersistent(Persistent*) override;
+  void VisitCollection(Collection*) override;
 
  protected:
   typedef std::deque<Edge*> Context;
   Context& context() { return context_; }
   Edge* Parent() { return context_.empty() ? 0 : context_.front(); }
   void Enter(Edge* e) { return context_.push_front(e); }
   void Leave() { context_.pop_front(); }
 
   // Default callback to overwrite in visitor subclass.
   virtual void AtValue(Value*);
@@ skipping 177 matching lines @@
   }
 
  private:
   RecordInfo* info_;
   Members members_;
   bool on_heap_;
   bool is_root_;
 };
 
 #endif  // TOOLS_BLINK_GC_PLUGIN_EDGE_H_