Bug 1009263 - Add nsCheapSets::Clear() method that removes all entries and return it to minimal size in terms of memory use. r=bsmedberg

xpcom/ds/nsCheapSets.h

@@ -24,6 +24,14 @@ public:
   {
   }
   ~nsCheapSet()
+  {
+    Clear();
+  }
+
+  /**
+   * Remove all entries.
+   */
+  void Clear()
   {
     switch (mState) {
     case ZERO:
@@ -38,6 +46,7 @@ public:
       NS_NOTREACHED("bogus state");
       break;
     }
+    mState = ZERO;
   }
 
   nsresult Put(const KeyType aVal);