Slightly faster implementation of HashMap.hasStringValue() on most browser by using the 'in' keyword.

Suggested by: mmastrac


git-svn-id: https://google-web-toolkit.googlecode.com/svn/trunk@1572 8db76d5a-ed1c-0410-87a9-c151d255dfc7
diff --git a/user/super/com/google/gwt/emul/java/util/HashMap.java b/user/super/com/google/gwt/emul/java/util/HashMap.java
index fb49363..6b73659 100644
--- a/user/super/com/google/gwt/emul/java/util/HashMap.java
+++ b/user/super/com/google/gwt/emul/java/util/HashMap.java
@@ -343,7 +343,7 @@
    * Returns true if the given key exists in the stringMap.
    */
   private native boolean hasStringValue(String key) /*-{
-    return this.@java.util.HashMap::stringMap[':' + key] !== undefined ;
+    return (':' + key) in this.@java.util.HashMap::stringMap;
   }-*/;
   
   /**