Add stackTrace to Error object.

runtime/lib/error.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.
 // Errors are created and thrown by DartVM only.
 // Changes here should also be reflected in corelib/error.dart as well
 
-class AssertionErrorImplementation implements AssertionError {
+class AssertionErrorImplementation extends AssertionError {
   factory AssertionErrorImplementation._uninstantiable() {
     throw new UnsupportedError(
         "AssertionError can only be allocated by the VM");
   }
   static _throwNew(int assertionStart, int assertionEnd)
       native "AssertionError_throwNew";
   String toString() {
     return "'$url': Failed assertion: line $line pos $column: "
         "'$failedAssertion' is not true.";
   }
@@ skipping 46 matching lines @@
     if ((dstName != null) && (dstName.length > 0)) {
       str = "${str}type '$srcType' is not a subtype of "
             "type '$dstType' in type cast.";
     } else {
       str = "${str}malformed type used in type cast.";
     }
     return str;
   }
 }
 
-class FallThroughErrorImplementation implements FallThroughError {
+class FallThroughErrorImplementation extends FallThroughError {
   factory FallThroughErrorImplementation._uninstantiable() {
     throw new UnsupportedError(
         "FallThroughError can only be allocated by the VM");
   }
   static _throwNew(int case_clause_pos) native "FallThroughError_throwNew";
   String toString() {
     return "'$url': Switch case fall-through at line $line.";
   }
   final String url;
   final int line;
 }
 
 class InternalError {
   const InternalError(this._msg);
   String toString() => "InternalError: '${_msg}'";
   final String _msg;
 }
 
 
 class AbstractClassInstantiationErrorImplementation
-    implements AbstractClassInstantiationError {
+    extends AbstractClassInstantiationError {
 
   factory AbstractClassInstantiationErrorImplementation._uninstantiable() {
     throw new UnsupportedError(
         "AbstractClassInstantiationError can only be allocated by the VM");
   }
 
   static _throwNew(int case_clause_pos, String className)
       native "AbstractClassInstantiationError_throwNew";
 
   String toString() {
     return "Cannot instantiate abstract class $className: "
            "url '$url' line $line";
   }
 
   final String className;
   final String url;
   final int line;
 }