Reland #2: Add a short term solution to fix OSX 10.11 system font rendering problems.

Source/platform/mac/VersionUtilMac.h

Index: Source/platform/mac/VersionUtilMac.h
diff --git a/Source/platform/mac/VersionUtilMac.h b/Source/platform/mac/VersionUtilMac.h
index 2eee2d069fe26637c7b2def4742d9f93a0f3c74a..6be479880ee2b8a4cc36f98e54b13823339ca34a 100644
--- a/Source/platform/mac/VersionUtilMac.h
+++ b/Source/platform/mac/VersionUtilMac.h
@@ -16,6 +16,12 @@ PLATFORM_EXPORT bool IsOSLionOrEarlier();
 PLATFORM_EXPORT bool IsOSMavericksOrEarlier();
 PLATFORM_EXPORT bool IsOSMavericks();
 
+// Yosemite is Mac OS X 10.10, Darwin 14.
+PLATFORM_EXPORT bool IsOSYosemite();
+
+// El Capitan is Mac OS X 10.11, Darwin 15.
+PLATFORM_EXPORT bool IsOSElCapitan();
+
 } // namespace blink
 
 #endif // VersionUtilMac_h