[Mac] Refactor the logic of tab dragging out of TabView and into a new helper.

chrome/browser/ui/cocoa/tabs/tab_controller.h

 // Copyright (c) 2011 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 CHROME_BROWSER_UI_COCOA_TABS_TAB_CONTROLLER_H_
 #define CHROME_BROWSER_UI_COCOA_TABS_TAB_CONTROLLER_H_
 #pragma once
 
 #import <Cocoa/Cocoa.h>
 #import "chrome/browser/ui/cocoa/hover_close_button.h"
+#import "chrome/browser/ui/cocoa/tabs/tab_strip_drag_controller.h"
 #include "chrome/browser/ui/tabs/tab_menu_model.h"
 #include "googleurl/src/gurl.h"
 
 // The loading/waiting state of the tab.
 enum TabLoadingState {
   kTabDone,
   kTabLoading,
   kTabWaiting,
   kTabCrashed,
 };
 
 @class MenuController;
 namespace TabControllerInternal {
 class MenuDelegate;
 }
 @class TabView;
 @protocol TabControllerTarget;
 
 // A class that manages a single tab in the tab strip. Set its target/action
 // to be sent a message when the tab is selected by the user clicking. Setting
 // the |loading| property to YES visually indicates that this tab is currently
 // loading content via a spinner.
 //
 // The tab has the notion of an "icon view" which can be used to display
 // identifying characteristics such as a favicon, or since it's a full-fledged
 // view, something with state and animation such as a throbber for illustrating
 // progress. The default in the nib is an image view so nothing special is
 // required if that's all you need.
 
-@interface TabController : NSViewController {
+@interface TabController : NSViewController<TabDraggingEventTarget> {
  @private
   IBOutlet NSView* iconView_;
   IBOutlet NSTextField* titleView_;
   IBOutlet HoverCloseButton* closeButton_;
 
   NSRect originalIconFrame_;  // frame of iconView_ as loaded from nib
   BOOL isIconShowing_;  // last state of iconView_ in updateVisibility
 
   BOOL app_;
   BOOL mini_;
@@ skipping 63 matching lines @@
 @end
 
 @interface TabController(TestingAPI)
 - (NSString*)toolTip;
 - (int)iconCapacity;
 - (BOOL)shouldShowIcon;
 - (BOOL)shouldShowCloseButton;
 @end  // TabController(TestingAPI)
 
 #endif  // CHROME_BROWSER_UI_COCOA_TABS_TAB_CONTROLLER_H_