Remove methods on StackTrace class.

sdk/lib/_internal/compiler/implementation/lib/js_helper.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.
 
 library _js_helper;
 
 import 'dart:collection';
 import 'dart:_foreign_helper' show DART_CLOSURE_TO_JS,
                                    JS,
                                    JS_CALL_IN_ISOLATE,
@@ skipping 806 matching lines @@
   // the exception comes from the DOM, it is a JavaScript
   // object backed by a native Dart class.
   return ex;
 }
 
 /**
  * Called by generated code to fetch the stack trace from an
  * exception.
  */
 StackTrace getTraceFromException(exception) {
-  return new StackTrace(JS("var", r"#.stack", exception));
+  return new _StackTrace(JS("var", r"#.stack", exception));
 }
 
-class StackTrace {
-  var stack;
-  StackTrace(this.stack);
-  String toString() => stack != null ? stack : '';
+class _StackTrace implements StackTrace {
+  var _stack;
+  _StackTrace(this._stack);
+  String toString() => _stack != null ? _stack : '';
 }
 
 
 /**
  * Called by generated code to build a map literal. [keyValuePairs] is
  * a list of key, value, key, value, ..., etc.
  */
 makeLiteralMap(List keyValuePairs) {
   Iterator iterator = keyValuePairs.iterator;
   Map result = new LinkedHashMap();
@@ skipping 527 matching lines @@
                               expectedArgumentNames);
 }
 
 /**
  * Called by generated code when a static field's initializer references the
  * field that is currently being initialized.
  */
 void throwCyclicInit(String staticName) {
   throw new RuntimeError("Cyclic initialization for static $staticName");
 }