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

Source/platform/mac/VersionUtilMac.mm

Index: Source/platform/mac/VersionUtilMac.mm
diff --git a/Source/platform/mac/VersionUtilMac.mm b/Source/platform/mac/VersionUtilMac.mm
index 29e22f995fbad849512194e6dae6a454c6b8e8e5..4e483b7270d35d13a8b1bf24727228762715496f 100644
--- a/Source/platform/mac/VersionUtilMac.mm
+++ b/Source/platform/mac/VersionUtilMac.mm
@@ -11,6 +11,10 @@
 #define NSAppKitVersionNumber10_9 1265
 #endif
 
+#ifndef NSAppKitVersionNumber10_10
+#define NSAppKitVersionNumber10_10 1343
+#endif
+
 namespace blink {
 
 bool IsOSMavericksOrEarlier()
@@ -23,4 +27,14 @@ bool IsOSMavericks()
     return floor(NSAppKitVersionNumber) == NSAppKitVersionNumber10_9;
 }
 
+bool IsOSYosemiteOrEarlier()
+{
+    return floor(NSAppKitVersionNumber) <= NSAppKitVersionNumber10_10;
+}
+
+bool IsOSYosemite()
+{
+    return floor(NSAppKitVersionNumber) == NSAppKitVersionNumber10_10;
+}
+
 } // namespace blink