mac: Fix a newly introduced history swiping bug.

base/mac/sdk_forward_declarations.h

 // Copyright (c) 2012 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.
 
 // This file contains forward declarations for items in later SDKs than the
 // default one with which Chromium is built (currently 10.6).
 // If you call any function from this header, be sure to check at runtime for
 // respondsToSelector: before calling these functions (else your code will crash
 // on older OS X versions that chrome still supports).
 
 #ifndef BASE_MAC_SDK_FORWARD_DECLARATIONS_H_
 #define BASE_MAC_SDK_FORWARD_DECLARATIONS_H_
 
 #import <AppKit/AppKit.h>
 
 #if !defined(MAC_OS_X_VERSION_10_7) || \
     MAC_OS_X_VERSION_MAX_ALLOWED < MAC_OS_X_VERSION_10_7
 enum {
   NSEventPhaseNone        = 0, // event not associated with a phase.
   NSEventPhaseBegan       = 0x1 << 0,
   NSEventPhaseStationary  = 0x1 << 1,
   NSEventPhaseChanged     = 0x1 << 2,
   NSEventPhaseEnded       = 0x1 << 3,
   NSEventPhaseCancelled   = 0x1 << 4,
+  NSEventPhaseMayBegin    = 0x1 << 5
 };
 typedef NSUInteger NSEventPhase;
 
 enum {
   NSEventSwipeTrackingLockDirection = 0x1 << 0,
   NSEventSwipeTrackingClampGestureAmount = 0x1 << 1,
 };
 typedef NSUInteger NSEventSwipeTrackingOptions;
 
 enum {
@@ skipping 34 matching lines @@
 @end
 
 @interface NSWindow (LionSDK)
 - (CGFloat)backingScaleFactor;
 - (NSWindowAnimationBehavior)animationBehavior;
 - (void)setAnimationBehavior:(NSWindowAnimationBehavior)newAnimationBehavior;
 @end
 #endif  // MAC_OS_X_VERSION_10_7
 
 #endif  // BASE_MAC_SDK_FORWARD_DECLARATIONS_H_