mac: Move more 10.7 api stuff into sdk_forward_declarations.h

ui/snapshot/snapshot_mac_unittest.mm

Index: ui/snapshot/snapshot_mac_unittest.mm
diff --git a/ui/snapshot/snapshot_mac_unittest.mm b/ui/snapshot/snapshot_mac_unittest.mm
index 900617335a820c878bfa976c9bedc22bc806ff80..362902e3ce7ab9da2280cefc1cb2bdc11bbb2592 100644
--- a/ui/snapshot/snapshot_mac_unittest.mm
+++ b/ui/snapshot/snapshot_mac_unittest.mm
@@ -6,20 +6,12 @@
 
 #import <Cocoa/Cocoa.h>
 
+#include "base/mac/sdk_forward_declarations.h"
 #include "base/memory/scoped_nsobject.h"
 #include "base/memory/scoped_ptr.h"
 #include "testing/platform_test.h"
 #include "ui/gfx/rect.h"
 
-#if !defined(MAC_OS_X_VERSION_10_7) || \
-    MAC_OS_X_VERSION_MAX_ALLOWED < MAC_OS_X_VERSION_10_7
-
-@interface NSWindow (LionAPI)
-- (CGFloat)backingScaleFactor;
-@end
-
-#endif  // 10.7
-
 namespace ui {
 namespace {