ChangeScreen2: Auto-focus to submit button

After scoring a change with a maximum value in a radio group focus to
the submit button if it is enabled.  This allows committers to submit
a change with just Return/Enter/Space after posting Code-Review+2.

Change-Id: Ide28d62c24cfe7fd7e044d8b3b74ac5d246b8739

gerrit-gwtui/src/main/java/com/google/gerrit/client/changes/ReviewInput.java

@@ -36,6 +36,7 @@ public class ReviewInput extends JavaScriptObject {
 
   public final native void message(String m) /*-{ if(m)this.message=m; }-*/;
   public final native void label(String n, short v) /*-{ this.labels[n]=v; }-*/;
+  public final native short label(String n) /*-{ return this.labels[n]||0 }-*/;
   public final native void comments(NativeMap<JsArray<CommentInfo>> m)
   /*-{ this.comments=m }-*/;