Mac: Support default browser Handoff in Yosemite.

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).
 
@@ skipping 236 matching lines @@
   NSWindowOcclusionStateVisible = 1UL << 1,
 };
 typedef NSUInteger NSWindowOcclusionState;
 
 @interface NSWindow (MavericksSDK)
 - (NSWindowOcclusionState)occlusionState;
 @end
 
 #endif  // MAC_OS_X_VERSION_10_9
 
+#if !defined(MAC_OS_X_VERSION_10_10) || \
+    MAC_OS_X_VERSION_MAX_ALLOWED < MAC_OS_X_VERSION_10_10
+
+@interface NSUserActivity : NSObject
+
+@property (readonly, copy) NSString* activityType;
+@property (copy) NSURL* webPageURL;
+
+@end
+
+BASE_EXPORT extern "C" NSString* const NSUserActivityTypeBrowsingWeb;
+
+#endif  // MAC_OS_X_VERSION_10_10
+
 #endif  // BASE_MAC_SDK_FORWARD_DECLARATIONS_H_