[Mac] Rely on science, not chance, to get the proper definition of the macro

Source/platform/geometry/IntSize.h

Index: Source/platform/geometry/IntSize.h
diff --git a/Source/platform/geometry/IntSize.h b/Source/platform/geometry/IntSize.h
index 8b7a582ffe5c5df0e901427f7931823bc1469414..42a977973437b7f9670f13ccb8a0e8490c4f6d0a 100644
--- a/Source/platform/geometry/IntSize.h
+++ b/Source/platform/geometry/IntSize.h
@@ -32,10 +32,8 @@
 #if OS(MACOSX)
 typedef struct CGSize CGSize;
 
-#ifdef NSGEOMETRY_TYPES_SAME_AS_CGGEOMETRY_TYPES
-typedef struct CGSize NSSize;
-#else
-typedef struct _NSSize NSSize;
+#ifdef __OBJC__
+#import <Foundation/Foundation.h>
 #endif
 #endif
 
@@ -118,7 +116,7 @@ public:
     explicit IntSize(const CGSize&); // don't do this implicitly since it's lossy
     operator CGSize() const;
 
-#if !defined(NSGEOMETRY_TYPES_SAME_AS_CGGEOMETRY_TYPES)
+#if defined(__OBJC__) && !defined(NSGEOMETRY_TYPES_SAME_AS_CGGEOMETRY_TYPES)
     explicit IntSize(const NSSize &); // don't do this implicitly since it's lossy
     operator NSSize() const;
 #endif