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

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

 // 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.
 
 #include "base/mac/mac_util.h"
 #import "chrome/browser/themes/theme_service.h"
 #import "chrome/browser/ui/cocoa/menu_controller.h"
 #import "chrome/browser/ui/cocoa/tabs/tab_controller.h"
 #import "chrome/browser/ui/cocoa/tabs/tab_controller_target.h"
 #import "chrome/browser/ui/cocoa/tabs/tab_view.h"
@@ skipping 301 matching lines @@
 
 // Called by the tabs to determine whether we are in rapid (tab) closure mode.
 - (BOOL)inRapidClosureMode {
   if ([[self target] respondsToSelector:@selector(inRapidClosureMode)]) {
     return [[self target] performSelector:@selector(inRapidClosureMode)] ?
         YES : NO;
   }
   return NO;
 }
 
+// The following methods are invoked from the TabView and are forwarded to the
+// TabStripDragController.
+- (BOOL)tabCanBeDragged:(TabController*)controller {
+  return [[target_ dragController] tabCanBeDragged:controller];
+}
+
+- (void)maybeStartDrag:(NSEvent*)event forTab:(TabController*)tab {
+  [[target_ dragController] maybeStartDrag:event forTab:tab];
+}
+
+- (void)continueDrag:(NSEvent*)event {
+  [[target_ dragController] continueDrag:event];
+}
+
+- (void)endDrag:(NSEvent*)event {
+  [[target_ dragController] endDrag:event];
+}
+
 @end