Make user shortcuts override built-in shortcuts.

chrome/browser/tab_contents/tab_contents_view_mac.mm

 // Copyright (c) 2006-2008 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 <Carbon/Carbon.h>
 
 #include "chrome/browser/tab_contents/tab_contents_view_mac.h"
 
 #include <string>
 
@@ skipping 315 matching lines @@
   // If this tab is no longer active, its window will be |nil|. In that case,
   // best ignore the event.
   if (![self window])
     return;
   ChromeEventProcessingWindow* window =
       (ChromeEventProcessingWindow*)[self window];
   DCHECK([window isKindOfClass:[ChromeEventProcessingWindow class]]);
 
   // Do not fire shortcuts on key up.
   if ([event type] == NSKeyDown) {
+    // Send the event to the menu before sending it to the browser/window
+    // shortcut handling, so that if a user configures cmd-left to mean
+    // "previous tab", it takes precedence over the built-in "history back"
+    // binding. Other than that, the |redispatchEvent| call would take care of
+    // invoking the original menu item shortcut as well.
+    if ([[NSApp mainMenu] performKeyEquivalent:event])
+      return;
+
     if ([window handleExtraBrowserKeyboardShortcut:event])
       return;
     if ([window handleExtraWindowKeyboardShortcut:event])
       return;
   }
 
   // We need to re-dispatch the event, so that it is sent to the menu or other
   // cocoa mechanisms (such as the cmd-` handler).
   RenderWidgetHostViewCocoa* rwhv = static_cast<RenderWidgetHostViewCocoa*>(
       tabContentsView_->GetContentNativeView());
@@ skipping 108 matching lines @@
 }
 
 - (BOOL)performDragOperation:(id<NSDraggingInfo>)sender {
   return [dropTarget_ performDragOperation:sender view:self];
 }
 
 // Tons of stuff goes here, where we grab events going on in Cocoaland and send
 // them into the C++ system. TODO(avi): all that jazz
 
 @end