Adds @SpecializeMethod to AbstractHashMap.containsKey()

Change-Id: I1fc3919131da6f5f5b7434e19c176c506501b3d8

user/super/com/google/gwt/emul/java/util/AbstractHashMap.java

diff --git a/user/super/com/google/gwt/emul/java/util/AbstractHashMap.java b/user/super/com/google/gwt/emul/java/util/AbstractHashMap.java
index a186c98..3fa35b4 100644
--- a/user/super/com/google/gwt/emul/java/util/AbstractHashMap.java
+++ b/user/super/com/google/gwt/emul/java/util/AbstractHashMap.java
@@ -211,6 +211,7 @@
     clearImpl();
   }
 
+  @SpecializeMethod(params = {String.class}, target = "hasStringValue")
   @Override
   public boolean containsKey(Object key) {
     return (key == null) ? nullSlotLive : (!(key instanceof String)
@@ -413,7 +414,10 @@
   /**
    * Returns true if the given key exists in the stringMap.
    */
-  private native boolean hasStringValue(String key) /*-{
+  protected native boolean hasStringValue(String key) /*-{
+    if (key == null) {
+      return this.@java.util.AbstractHashMap::nullSlotLive;
+    }
     return (':' + key) in this.@java.util.AbstractHashMap::stringMap;
   }-*/;