[Mac] Add two-finger gesture support for Lion, which respects the system preference.

chrome/browser/ui/cocoa/browser_window_controller_private.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.
 
 #import "chrome/browser/ui/cocoa/browser_window_controller_private.h"
 
 #include "base/command_line.h"
+#include "base/mac/mac_util.h"
 #import "base/memory/scoped_nsobject.h"
 #include "chrome/browser/browser_process.h"
 #include "chrome/browser/prefs/pref_service.h"
 #include "chrome/browser/prefs/scoped_user_pref_update.h"
 #include "chrome/browser/profiles/profile.h"
 #include "chrome/browser/ui/bookmarks/bookmark_tab_helper.h"
 #include "chrome/browser/ui/browser_list.h"
 #import "chrome/browser/ui/cocoa/fast_resize_view.h"
 #import "chrome/browser/ui/cocoa/find_bar/find_bar_cocoa_controller.h"
 #import "chrome/browser/ui/cocoa/floating_bar_backing_view.h"
@@ skipping 518 matching lines @@
     return;
 
   barVisibilityUpdatesEnabled_ = NO;
   [fullscreenController_ cancelAnimationAndTimers];
 }
 
 - (void)setUpOSFullScreenButton {
   // TOOD(rsesek): Properly implement Lion fullscreen <http://crbug.com/74065>.
 }
 
+- (BOOL)recognizeTwoFingerGestures {
+  // Lion or higher will have support for two-finger swipe gestures.
+  if (!base::mac::IsOSLionOrLater())
+    return NO;
+
+  // A note about preferences:
+  // On Lion System Preferences, the swipe gesture behavior is controlled by the
+  // setting in Trackpad --> More Gestures --> Swipe between pages. This setting
+  // has three values:
+  //  A) Scroll left or right with two fingers. This should perform a cool
+  //     scrolling animation, but doesn't yet <http://crbug.com/90228>.
+  //  B) Swipe left or right with three fingers.
+  //  C) Swipe with two or three fingers.
+  //
+  // The three-finger gesture is controlled by the integer preference
+  // |com.apple.trackpad.threeFingerHorizSwipeGesture|. Its value is 0 for (A)
+  // and 1 for (B, C).
+  //
+  // The two-finger gesture is controlled by the preference below and is boolean
+  // YES for (A, C) and NO for (B).
+  NSUserDefaults* defaults = [NSUserDefaults standardUserDefaults];
+  return [defaults boolForKey:@"AppleEnableSwipeNavigateWithScrolls"];
+}
+
 @end  // @implementation BrowserWindowController(Private)