Change signature of lookupConstructor to only require a name.

pkg/compiler/lib/src/elements/modelx.dart

Index: pkg/compiler/lib/src/elements/modelx.dart
diff --git a/pkg/compiler/lib/src/elements/modelx.dart b/pkg/compiler/lib/src/elements/modelx.dart
index 007e58482e9c7fbdbee9805c16f1c56679984a8b..27fdf7d8bfe42437483f470ecf4b59e155aabcf8 100644
--- a/pkg/compiler/lib/src/elements/modelx.dart
+++ b/pkg/compiler/lib/src/elements/modelx.dart
@@ -2193,12 +2193,18 @@ abstract class BaseClassElementX extends ElementX
     return result;
   }
 
-  // TODO(aprelev@gmail.com): Peter believes that it would be great to
-  // make noMatch a required argument. Peter's suspicion is that most
-  // callers of this method would benefit from using the noMatch method.
-  Element lookupConstructor(Selector selector, [Element noMatch(Element)]) {
-    Element result = localLookup(selector.name);
-    return validateConstructorLookupResults(selector, result, noMatch);
+  ConstructorElement lookupDefaultConstructor() {
+    ConstructorElement constructor = lookupConstructor("");
+    if (constructor != null
+        && constructor.functionSignature.requiredParameterCount == 0) {
+      return constructor;
+    }
+    return null;
+  }
+
+  ConstructorElement lookupConstructor(String name) {
+    Element result = localLookup(name);
+    return result != null && result.isConstructor ? result : null;
   }
 
   Link<Element> get constructors {