Made dart2js constructor lookup logic "private"-aware, fixed 4740 bug.

lib/compiler/implementation/resolver.dart

Index: lib/compiler/implementation/resolver.dart
diff --git a/lib/compiler/implementation/resolver.dart b/lib/compiler/implementation/resolver.dart
index 4d48866514c95619f2f715eece5cae4ee62aa3b9..ff83d263582b2d6faa9f288c9081ccba73566ffa 100644
--- a/lib/compiler/implementation/resolver.dart
+++ b/lib/compiler/implementation/resolver.dart
@@ -89,7 +89,12 @@ class ResolverTask extends CompilerTask {
       final SourceString constructorName =
           getConstructorName(initializers.head);
       final SourceString className = classElement.name;
-      return classElement.lookupConstructor(className, constructorName);
+
+      return classElement.lookupConstructor(
+          new Selector.callConstructor(
+              new SelectorName.namedConstructor(className, constructorName),
+              constructor.getLibrary())
+          );
     }
     return null;
   }
@@ -185,7 +190,10 @@ class ResolverTask extends CompilerTask {
     } else {
       name = constructor.name;
     }
-    constructor.defaultImplementation = defaultClass.lookupConstructor(name);
+    constructor.defaultImplementation = defaultClass.lookupConstructor(
+        new Selector.callConstructor(
+            new SelectorName.namedClass(name),
+            defaultClass.getLibrary()));
 
     if (constructor.defaultImplementation === null) {
       // We failed to find a constructor named either
@@ -592,7 +600,10 @@ class InitializerResolver {
     // Lookup constructor and try to match it to the selector.
     ResolverTask resolver = visitor.compiler.resolver;
     final SourceString className = lookupTarget.name;
-    result = lookupTarget.lookupConstructor(className, constructorName);
+    result = lookupTarget.lookupConstructor(
+        new Selector.callConstructor(
+            new SelectorName.namedConstructor(className, constructorName),
+            constructor.getLibrary()));
     if (result === null || !result.isGenerativeConstructor()) {
       String classNameString = className.slowToString();
       String constructorNameString = constructorName.slowToString();
@@ -2604,7 +2615,10 @@ class ConstructorResolver extends CommonResolverVisitor<Element> {
                                     Node diagnosticNode,
                                     SourceString constructorName) {
     cls.ensureResolved(compiler);
-    Element result = cls.lookupConstructor(cls.name, constructorName);
+    Element result = cls.lookupConstructor(
+        new Selector.callConstructor(
+            new SelectorName.namedConstructor(cls.name, constructorName),
+            resolver.enclosingElement.getLibrary()));
     if (result === null) {
       String fullConstructorName = cls.name.slowToString();
       if (constructorName !== const SourceString('')) {