Forward-declare enums in a way that is compatible with NS_ENUM

base/mac/foundation_util.h

Index: base/mac/foundation_util.h
diff --git a/base/mac/foundation_util.h b/base/mac/foundation_util.h
index 0d78c554fb31076577e9d087cc7084959a6f65ea..447f7bf0d8921781fc9592ec10e048d224289126 100644
--- a/base/mac/foundation_util.h
+++ b/base/mac/foundation_util.h
@@ -28,12 +28,22 @@ class NSString;
 #include <ApplicationServices/ApplicationServices.h>
 #endif
 
+// Adapted from NSObjCRuntime.h NS_ENUM definition (used in Foundation starting
+// with the OS X 10.8 SDK and the iOS 6.0 SDK).
+#if __has_extension(cxx_strong_enums) && \
+    (defined(OS_IOS) || (defined(MAC_OS_X_VERSION_10_8) && \
+                         MAC_OS_X_VERSION_MAX_ALLOWED >= MAC_OS_X_VERSION_10_8))
+#define CR_FORWARD_ENUM(_type, _name) enum _name : _type _name
+#else
+#define CR_FORWARD_ENUM(_type, _name) _type _name
+#endif
+
 // Adapted from NSPathUtilities.h and NSObjCRuntime.h.
 #if __LP64__ || NS_BUILD_32_LIKE_64
-typedef unsigned long NSSearchPathDirectory;
+typedef CR_FORWARD_ENUM(unsigned long, NSSearchPathDirectory);
 typedef unsigned long NSSearchPathDomainMask;
 #else
-typedef unsigned int NSSearchPathDirectory;
+typedef CR_FORWARD_ENUM(unsigned int, NSSearchPathDirectory);
 typedef unsigned int NSSearchPathDomainMask;
 #endif