Factor out GamepadCommon base class from Gamepad and WebKitGamepad

Source/modules/gamepad/WebKitGamepadList.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 WebKitGamepadList_h
 #define WebKitGamepadList_h
 
 #include "bindings/v8/ScriptWrappable.h"
 #include "heap/Handle.h"
 #include "modules/gamepad/WebKitGamepad.h"
 #include "public/platform/WebGamepads.h"
 #include "wtf/PassRefPtr.h"
 #include "wtf/RefCounted.h"
 #include "wtf/Vector.h"
 
 namespace WebCore {
 
-class WebKitGamepadList : public RefCountedWillBeGarbageCollectedFinalized<WebKitGamepadList>, public ScriptWrappable {
+class WebKitGamepadList FINAL : public RefCountedWillBeGarbageCollectedFinalized<WebKitGamepadList>, public ScriptWrappable {
 public:
-    static PassRefPtrWillBeRawPtr<WebKitGamepadList> create() { return adoptRefWillBeNoop(new WebKitGamepadList); }
+    static PassRefPtrWillBeRawPtr<WebKitGamepadList> create()
+    {
+        return adoptRefWillBeNoop(new WebKitGamepadList);
+    }
     ~WebKitGamepadList();
 
     void set(unsigned index, PassRefPtrWillBeRawPtr<WebKitGamepad>);
     WebKitGamepad* item(unsigned index);
-    unsigned length() const;
+    unsigned length() const { return blink::WebGamepads::itemsLengthCap; }
 
     void trace(Visitor*);
 
 private:
-    WebKitGamepadList()
-    {
-        ScriptWrappable::init(this);
-    }
-
+    WebKitGamepadList();
     RefPtrWillBeMember<WebKitGamepad> m_items[blink::WebGamepads::itemsLengthCap];
 };
 
 } // namespace WebCore
 
 #endif // WebKitGamepadList_h