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

chrome/browser/ui/cocoa/browser_window_controller.h

Index: chrome/browser/ui/cocoa/browser_window_controller.h
diff --git a/chrome/browser/ui/cocoa/browser_window_controller.h b/chrome/browser/ui/cocoa/browser_window_controller.h
index f36a9a9a150c7b43b5ee66bd942e56d3e34c1e3d..5c11b8e6d96c02df835c8a639fe05627ae158c04 100644
--- a/chrome/browser/ui/cocoa/browser_window_controller.h
+++ b/chrome/browser/ui/cocoa/browser_window_controller.h
@@ -47,7 +47,6 @@ class TabContents;
 @class TabStripView;
 @class ToolbarController;
 
-
 @interface BrowserWindowController :
   TabWindowController<NSUserInterfaceValidations,
                       BookmarkBarControllerDelegate,
@@ -96,6 +95,12 @@ class TabContents;
   // NO on growth.
   BOOL isShrinkingFromZoomed_;
 
+  // Touch event data for two-finger gestures. Only available on Lion or higher
+  // with two-finger gestures enabled in the Trackpad preferences. This will
+  // contain the NSTouch objects from |-beginGestureWithEvent:| keyed by the
+  // touch's |identity|.
+  scoped_nsobject<NSMutableDictionary> twoFingerGestureTouches_;
+
   // The raw accumulated zoom value and the actual zoom increments made for an
   // an in-progress pinch gesture.
   CGFloat totalMagnifyGestureAmount_;