Reland #1: Add a short term solution to fix OSX 10.11 system font rendering problems.

Source/platform/mac/VersionUtilMac.mm

 // Copyright 2015 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 "config.h"
 #import "platform/mac/VersionUtilMac.h"
 
 #import <AppKit/AppKit.h>
 
 #ifndef NSAppKitVersionNumber10_9
 #define NSAppKitVersionNumber10_9 1265
 #endif
 
+#ifndef NSAppKitVersionNumber10_10
+#define NSAppKitVersionNumber10_10 1343
+#endif
+
 namespace blink {
 
 bool IsOSMavericksOrEarlier()
 {
     return floor(NSAppKitVersionNumber) <= NSAppKitVersionNumber10_9;
 }
 
 bool IsOSMavericks()
 {
     return floor(NSAppKitVersionNumber) == NSAppKitVersionNumber10_9;
 }
 
+bool IsOSYosemiteOrEarlier()
+{
+    return floor(NSAppKitVersionNumber) <= NSAppKitVersionNumber10_10;
+}
+
+bool IsOSYosemite()
+{
+    return floor(NSAppKitVersionNumber) == NSAppKitVersionNumber10_10;
+}
+
 } // namespace blink