Bug 1123237 - Part 10. Expose SwapElements from nsBaseHashtable. r=nfroyd

xpcom/glue/nsBaseHashtable.h

@@ -297,6 +297,15 @@ public:
     return aMallocSizeOf(this) + ShallowSizeOfExcludingThis(aMallocSizeOf);
   }
 
+  /**
+   * Swap the elements in this hashtable with the elements in aOther.
+   */
+  void SwapElements(nsBaseHashtable& aOther)
+  {
+    nsTHashtable<EntryType>::SwapElements(aOther);
+  }
+
+
 #ifdef DEBUG
   using nsTHashtable<EntryType>::MarkImmutable;
 #endif