Mac: Make middle-click tab closure cancellable.

chrome/browser/cocoa/tab_view.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.
 
 #import "chrome/browser/cocoa/tab_view.h"
 
 #include "base/logging.h"
 #include "base/nsimage_cache_mac.h"
 #import "chrome/browser/cocoa/tab_controller.h"
 #import "chrome/browser/cocoa/tab_window_controller.h"
@@ skipping 534 matching lines @@
   }
   [sourceController_ removePlaceholder];
   chromeIsVisible_ = YES;
 
   [self resetDragControllers];
 }
 
 - (void)otherMouseUp:(NSEvent*)theEvent {
   // Support middle-click-to-close.
   if ([theEvent buttonNumber] == 2) {
-    [controller_ closeTab:self];
+    // |-hitTest:| takes a location in the superview's coordinates.
+    NSPoint upLocation =
+        [[self superview] convertPoint:[theEvent locationInWindow]
+                              fromView:nil];
+    // If the mouse up occurred in our view or over the close button, then
+    // close.
+    if ([self hitTest:upLocation])
+      [controller_ closeTab:self];
   }
 }
 
 - (void)drawRect:(NSRect)rect {
   NSGraphicsContext* context = [NSGraphicsContext currentContext];
   [context saveGraphicsState];
   rect = [self bounds];
   BOOL active = [[self window] isKeyWindow] || [[self window] isMainWindow];
   BOOL selected = [(NSButton*)self state];
 
@@ skipping 149 matching lines @@
 }
 
 - (void)viewDidMoveToWindow {
   [super viewDidMoveToWindow];
   if ([self window]) {
     [controller_ updateTitleColor];
   }
 }
 
 @end