Fix warnings on Win64.

src/global-handles.h

 // Copyright 2007-2008 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 30 matching lines @@
 
 // Callback function on handling weak global handles.
 // typedef bool (*WeakSlotCallback)(Object** pointer);
 
 // An object group is treated like a single JS object: if one of object in
 // the group is alive, all objects in the same group are considered alive.
 // An object group is used to simulate object relationship in a DOM tree.
 class ObjectGroup : public Malloced {
  public:
   ObjectGroup() : objects_(4) {}
-  explicit ObjectGroup(size_t capacity) : objects_(capacity) {}
+  explicit ObjectGroup(size_t capacity)
+      : objects_(static_cast<int>(capacity)) { }
 
   List<Object**> objects_;
 };
 
 
 typedef void (*WeakReferenceGuest)(Object* object, void* parameter);
 
 class GlobalHandles : public AllStatic {
  public:
   // Creates a new global handle that is alive until Destroy is called.
@@ skipping 106 matching lines @@
   static Node* first_deallocated() { return first_deallocated_; }
   static void set_first_deallocated(Node* value) {
     first_deallocated_ = value;
   }
 };
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_GLOBAL_HANDLES_H_