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

Starting with the 10.8 SDK and the iOS 6.0 SDK, enums are declared
strongly typed in C++11 mode, which the old forward-declares weren't
compatible with. This creates a new macro for forward-declaring these
enums in a way that will match the SDK and compilation mode.

BUG=226494

Review URL: https://chromiumcodereview.appspot.com/13455004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@192543 0039d316-1c4b-4281-b951-d872f2087c98

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