Improve error handling of JS-calls

tests/compiler/dart2js/js_spec_string_test.dart

 // Copyright (c) 2014, 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.
 
 // Unit test of the [NativeBehavior.processSpecString] method.
 
 import 'package:expect/expect.dart';
 import 'package:compiler/src/native/native.dart';
 import 'package:compiler/src/dart2jslib.dart'
     show DiagnosticListener;
 import 'package:compiler/src/universe/universe.dart'
     show SideEffects;
 
 const OBJECT = 'Object';
 const NULL = 'Null';
 
 class Listener implements DiagnosticListener {
   String errorMessage;
   internalError(spannable, message) {
     errorMessage = message;
     throw "error";
   }
+  reportError(spannable, kind, arguments) {
+    errorMessage = '$arguments';  // E.g.  "{text: Duplicate tag 'new'.}"
+    throw "error";
+  }
 
   noSuchMethod(_) => null;
 }
 
 void test(String specString,
           {List returns,
            List creates,
            SideEffects expectedSideEffects,
            NativeThrowBehavior expectedThrows,
            bool expectedNew,
@@ skipping 13 matching lines @@
         specString,
         setSideEffects: (effects) { actualSideEffects = effects; },
         setThrows: (b) { actualThrows = b; },
         setIsAllocation: (b) { actualNew = b; },
         setUseGvn: (b) { actualGvn = b; },
         resolveType: (t) => t,
         typesReturned: actualReturns, typesInstantiated: actualCreates,
         objectType: OBJECT, nullType: NULL);
   } catch (e) {
     Expect.isTrue(expectError);
-    Expect.isNotNull(listener.errorMessage, 'Internal error expected.');
+    Expect.isNotNull(listener.errorMessage, 'Error expected.');
     return;
   }
-  Expect.isNull(listener.errorMessage, 'Unexpected internal error.');
+  Expect.isNull(listener.errorMessage, 'Unexpected error.');
   if (returns != null) {
     Expect.listEquals(returns, actualReturns, 'Unexpected returns.');
   }
   if (creates != null) {
     Expect.listEquals(creates, actualCreates, 'Unexpected creates.');
   }
   Expect.equals(expectedSideEffects, actualSideEffects);
   Expect.equals(expectedThrows, actualThrows);
   Expect.equals(expectedNew, actualNew);
   Expect.equals(expectedGvn, actualGvn);
@@ skipping 202 matching lines @@
   test('gvn:false', expectedGvn: false);
   test('returns:A;gvn:true', returns: ['A'], expectedGvn: true);
   test(' gvn : true ;  returns:A;', returns: ['A'], expectedGvn: true);
   test('gvn:true;returns:A;gvn:true', expectError: true);
 
   test('gvn: true; new: true', expectError: true);
   test('gvn: true; new: false', expectedGvn: true, expectedNew: false);
   test('gvn: false; new: true', expectedGvn: false, expectedNew: true);
   test('gvn: false; new: false', expectedGvn: false, expectedNew: false);
 }