dart2cps: Fix bug in constructors.

pkg/compiler/lib/src/cps_ir/cps_ir_builder_task.dart

 // Copyright (c) 2013, 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.
 
 library dart2js.ir_builder_task;
 
 import '../closure.dart' as closurelib;
 import '../closure.dart' hide ClosureScope;
 import '../constants/expressions.dart';
 import '../dart_types.dart';
@@ skipping 2563 matching lines @@
    * creates a new constructor body, if none can be found.
    *
    * Returns `null` if the constructor does not have a body.
    */
   ConstructorBodyElement getConstructorBody(FunctionElement constructor) {
     // TODO(asgerf): This is largely inherited from the SSA builder.
     // The ConstructorBodyElement has an invalid function signature, but we
     // cannot add a BoxLocal as parameter, because BoxLocal is not an element.
     // Instead of forging ParameterElements to forge a FunctionSignature, we
     // need a way to create backend methods without creating more fake elements.
-
+    constructor = constructor.implementation;

[floitsch, 2015/06/22 11:46:53]

I think we should always have implementations in the cps_ir_builder task.
From what I can see the constructor comes from a constructor-list, which in turn
is filled in evaluateConstructorFieldInitializers.
We should just get the implementation there.
(In my checkout this would be line 2437).

     assert(constructor.isGenerativeConstructor);
-    assert(invariant(constructor, constructor.isImplementation));
     if (constructor.isSynthesized) return null;
     ast.FunctionExpression node = constructor.node;
     // If we know the body doesn't have any code, we don't generate it.
     if (!node.hasBody()) return null;
     if (node.hasEmptyBody()) return null;
     ClassElement classElement = constructor.enclosingClass;
     ConstructorBodyElement bodyElement;
     classElement.forEachBackendMember((Element backendMember) {
       if (backendMember.isGenerativeConstructorBody) {
         ConstructorBodyElement body = backendMember;
@@ skipping 540 matching lines @@
   }
 
   processSetStatic(ir.SetStatic node) {
     node.body = replacementFor(node.body);
   }
 
   processContinuation(ir.Continuation node) {
     node.body = replacementFor(node.body);
   }
 }