Factor out GamepadCommon base class from Gamepad and WebKitGamepad

Source/modules/gamepad/WebKitGamepad.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 "config.h"
 #include "modules/gamepad/WebKitGamepad.h"
 
 namespace WebCore {
 
 WebKitGamepad::WebKitGamepad()
-    : m_index(0)
-    , m_timestamp(0)
 {
     ScriptWrappable::init(this);
 }
 
-void WebKitGamepad::setAxes(unsigned count, const float* data)
+WebKitGamepad::~WebKitGamepad()
 {
-    m_axes.resize(count);
-    if (count)
-        std::copy(data, data + count, m_axes.begin());
 }
 
 void WebKitGamepad::setButtons(unsigned count, const blink::WebGamepadButton* data)
 {
     m_buttons.resize(count);
     for (unsigned i = 0; i < count; ++i)
         m_buttons[i] = data[i].value;
 }
 
-void WebKitGamepad::trace(Visitor* visitor)
-{
-}
-
-WebKitGamepad::~WebKitGamepad()
-{
-}
-
 } // namespace WebCore