Bug 1399727 - Fix double-reporting of memory in ScriptPreloader. r=kmag.

DMD indicates double-reporting for mURL, indicating that it is shared.

--HG--
extra : rebase_source : b6e82cc3e4dbba9a59750b6be8117597034f23d7

js/xpconnect/loader/ScriptPreloader.h

@@ -269,8 +269,12 @@ private:
                 return size;
             }
 
-            size += (mURL.SizeOfExcludingThisEvenIfShared(mallocSizeOf) +
+            // Note: mURL and mCachePath use the same string for scripts loaded
+            // by the message manager. The following statement avoids
+            // double-measuring in that case.
+            size += (mURL.SizeOfExcludingThisIfUnshared(mallocSizeOf) +
                      mCachePath.SizeOfExcludingThisEvenIfShared(mallocSizeOf));
+
             return size;
         }