Improve and unify Mac OS X run-time version checks

base/mac/mac_util.h

Index: base/mac/mac_util.h
===================================================================
--- base/mac/mac_util.h	(revision 88826)
+++ base/mac/mac_util.h	(working copy)
@@ -110,6 +110,29 @@
 // 'Login Item' with 'hide on startup' flag. Used to suppress opening windows.
 bool WasLaunchedAsHiddenLoginItem();
 
+// Run-time OS version checks. Use these instead of
+// base::SysInfo::OperatingSystemVersionNumbers. Prefer the "OrEarlier" and
+// "OrLater" variants to those that check for a specific version, unless you
+// know for sure that you need to check for a specific version.
+
+// Leopard is Mac OS X 10.5, Darwin 9.
+bool IsOSLeopard();
+bool IsOSLeopardOrEarlier();
+
+// Snow Leopard is Mac OS X 10.6, Darwin 10.
+bool IsOSSnowLeopard();
+bool IsOSSnowLeopardOrEarlier();
+bool IsOSSnowLeopardOrLater();
+
+// Lion is Mac OS X 10.7, Darwin 11.
+bool IsOSLion();
+bool IsOSLionOrLater();
+
+// This should be infrequently used. It only makes sense to avoid codepaths
+// that are very likely to break on future (unreleased, untested, unborn) OS
+// releases.
+bool IsOSLaterThanLion();
+
 }  // namespace mac
 }  // namespace base