Start a drag if the tab is dragged off the sides of the window....

chrome/browser/cocoa/browser_window_controller.mm

 // Copyright (c) 2009 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 <Carbon/Carbon.h>
 
 #include "base/mac_util.h"
 #include "base/scoped_nsdisable_screen_updates.h"
 #import "base/scoped_nsobject.h"
 #include "base/sys_string_conversions.h"
@@ skipping 799 matching lines @@
                                  yStretchiness:yStretchiness];
 }
 
 - (void)removePlaceholder {
   [super removePlaceholder];
   [tabStripController_ insertPlaceholderForTab:nil
                                          frame:NSZeroRect
                                  yStretchiness:0];
 }
 
+- (BOOL)isTabFullyVisible:(TabView*)tab {
+  return [tabStripController_ isTabFullyVisible:tab];
+}
+
 - (void)showNewTabButton:(BOOL)show {
   [tabStripController_ showNewTabButton:show];
 }
 
 - (BOOL)isBookmarkBarVisible {
   return [[toolbarController_ bookmarkBarController] isBookmarkBarVisible];
 
 }
 
 - (void)toggleBookmarkBar {
@@ skipping 545 matching lines @@
       provider->GetNSColor(BrowserThemeProvider::COLOR_TOOLBAR);
   [theme setValue:toolbarBackgroundColor
      forAttribute:@"backgroundColor"
             style:GTMThemeStyleToolBar
             state:GTMThemeStateActiveWindow];
 
   return theme;
 }
 @end