Allow matchingTarget to also include the currentTarget.

tools/dom/templates/html/impl/impl_Event.darttemplate

Index: tools/dom/templates/html/impl/impl_Event.darttemplate
diff --git a/tools/dom/templates/html/impl/impl_Event.darttemplate b/tools/dom/templates/html/impl/impl_Event.darttemplate
index ef07e13c1cdca386238aa5b5f3202f5500e8ac03..2abce6290b3d4d7d7001c1895477385084d8bae5 100644
--- a/tools/dom/templates/html/impl/impl_Event.darttemplate
+++ b/tools/dom/templates/html/impl/impl_Event.darttemplate
@@ -50,13 +50,11 @@ $(ANNOTATIONS)$(CLASS_MODIFIERS)class $CLASSNAME$EXTENDS$IMPLEMENTS$NATIVESPEC {
     var currentTarget = this.currentTarget;
     var target = this.target;
     var matchedTarget;
-    while (matchedTarget == null && target != currentTarget && target != null) {
-      if (target.matches(_selector)) {
-        matchedTarget = target;
-      }
+    do {
+      if (target.matches(_selector)) return target;
       target = target.parent;
-    }
-    return matchedTarget;
+    } while (target != null && target != currentTarget.parent);
+    throw new StateError('No selector matched for populating matchedTarget.');
   }
 $!MEMBERS
 }