[Mac]Implement ViewID support. (third approach)

chrome/browser/cocoa/tab_strip_controller.h

 // Copyright (c) 2010 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_COCOA_TAB_STRIP_CONTROLLER_H_
 #define CHROME_BROWSER_COCOA_TAB_STRIP_CONTROLLER_H_
 
 #import <Cocoa/Cocoa.h>
 
 #include "base/scoped_nsobject.h"
@@ skipping 139 matching lines @@
 
 // Returns the index of the subview |view|. Returns -1 if not present. Takes
 // closing tabs into account such that this index will correctly match the tab
 // model. If |view| is in the process of closing, returns -1, as closing tabs
 // are no longer in the model.
 - (NSInteger)modelIndexForTabView:(NSView*)view;
 
 // Return the view at a given index.
 - (NSView*)viewAtIndex:(NSUInteger)index;
 
+// Return the number of tab views in the tab strip. It's same as number of tabs
+// in the model, except when a tab is closing, which will be counted in views
+// count, but no longer in the model.
+- (NSUInteger)viewsCount;
+
 // Set the placeholder for a dragged tab, allowing the |frame| and |strechiness|
 // to be specified. This causes this tab to be rendered in an arbitrary position
 - (void)insertPlaceholderForTab:(TabView*)tab
                           frame:(NSRect)frame
                   yStretchiness:(CGFloat)yStretchiness;
 
 // Returns whether or not |tab| can still be fully seen in the tab strip or if
 // its current position would cause it be obscured by things such as the edge
 // of the window or the window decorations. Returns YES only if the entire tab
 // is visible.
@@ skipping 43 matching lines @@
 - (void)removeConstrainedWindow:(ConstrainedWindowMac*)window;
 - (void)updateDevToolsForContents:(TabContents*)contents;
 
 @end
 
 // Notification sent when the number of tabs changes. The object will be this
 // controller.
 extern NSString* const kTabStripNumberOfTabsChanged;
 
 #endif  // CHROME_BROWSER_COCOA_TAB_STRIP_CONTROLLER_H_