Factor out GamepadCommon base class from Gamepad and WebKitGamepad

Source/modules/gamepad/GamepadList.h

Index: Source/modules/gamepad/GamepadList.h
diff --git a/Source/modules/gamepad/GamepadList.h b/Source/modules/gamepad/GamepadList.h
index b19e6afc5c042d2e2ff471da76bf39ceb9734733..363e5b9de05605bf559cbf4d60660835d394af8c 100644
--- a/Source/modules/gamepad/GamepadList.h
+++ b/Source/modules/gamepad/GamepadList.h
@@ -36,23 +36,22 @@
 
 namespace WebCore {
 
-class GamepadList : public RefCountedWillBeGarbageCollectedFinalized<GamepadList>, public ScriptWrappable {
+class GamepadList FINAL : public RefCountedWillBeGarbageCollectedFinalized<GamepadList>, public ScriptWrappable {
 public:
-    static PassRefPtrWillBeRawPtr<GamepadList> create() { return adoptRefWillBeNoop(new GamepadList); }
+    static PassRefPtrWillBeRawPtr<GamepadList> create()
+    {
+        return adoptRefWillBeNoop(new GamepadList);
+    }
     ~GamepadList();
 
     void set(unsigned index, PassRefPtrWillBeRawPtr<Gamepad>);
     Gamepad* item(unsigned index);
-    unsigned length() const;
+    unsigned length() const { return blink::WebGamepads::itemsLengthCap; }
 
     void trace(Visitor*);
 
 private:
-    GamepadList()
-    {
-        ScriptWrappable::init(this);
-    }
-
+    GamepadList();
     RefPtrWillBeMember<Gamepad> m_items[blink::WebGamepads::itemsLengthCap];
 };