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

tests/compiler/dart2js/resolver_test.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #import('dart:uri');
 
 #import("../../../lib/compiler/implementation/leg.dart");
 #import("../../../lib/compiler/implementation/elements/elements.dart");
 #import("../../../lib/compiler/implementation/tree/tree.dart");
 #import("../../../lib/compiler/implementation/scanner/scannerlib.dart");
@@ skipping 544 matching lines @@
 resolveConstructor(String script, String statement, String className,
                    String constructor, int expectedElementCount,
                    [List expectedWarnings = const [],
                     List expectedErrors = const [],
                     String corelib = DEFAULT_CORELIB]) {
   MockCompiler compiler = new MockCompiler(corelib);
   compiler.parseScript(script);
   compiler.resolveStatement(statement);
   ClassElement classElement =
       compiler.mainApp.find(buildSourceString(className));
-  Element element =
-      classElement.lookupConstructor(buildSourceString(constructor));
+  Element element = classElement.lookupConstructor(
+      new Selector.callDefaultConstructor(buildSourceString(constructor),
+                                          statement.getLibrary());
   FunctionExpression tree = element.parseNode(compiler);
   ResolverVisitor visitor = new ResolverVisitor(compiler, element);
   new InitializerResolver(visitor).resolveInitializers(element, tree);
   visitor.visit(tree.body);
   Expect.equals(expectedElementCount, map(visitor).length);
 
   compareWarningKinds(script, expectedWarnings, compiler.warnings);
   compareWarningKinds(script, expectedErrors, compiler.errors);
 }
 
@@ skipping 205 matching lines @@
         var d = new D();
         --d;
       }""";
   final compiler = compileScript(script);
 
   checkMemberResolved(compiler, 'A', operatorName('+', false));
   checkMemberResolved(compiler, 'B', operatorName('+', false));
   checkMemberResolved(compiler, 'C', operatorName('-', false));
   checkMemberResolved(compiler, 'D', operatorName('-', false));
 }