dart2js: reuse stack trace on rethrow

sdk/lib/_internal/compiler/js_lib/js_helper.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 _js_helper;
 
 import 'dart:_async_await_error_codes' as async_error_codes;
 
 import 'dart:_js_embedded_names' show
     DEFERRED_LIBRARY_URIS,
@@ skipping 2034 matching lines @@
 }
 
 /**
  * Called by generated code to fetch the stack trace from an
  * exception. Should never return null.
  */
 StackTrace getTraceFromException(exception) {
   if (exception is ExceptionAndStackTrace) {
     return exception.stackTrace;
   }
-  return new _StackTrace(exception);
+  if (exception == null) return new _StackTrace(exception);
+  _StackTrace trace = JS('_StackTrace|Null', r'#.$cachedTrace', exception);
+  if (trace != null) return trace;
+  trace = new _StackTrace(exception);
+  return JS('_StackTrace', r'#.$cachedTrace = #', exception, trace);
 }
 
 class _StackTrace implements StackTrace {
   var _exception;
   String _trace;
   _StackTrace(this._exception);
 
   String toString() {
     if (_trace != null) return JS('String', '#', _trace);
 
@@ skipping 2023 matching lines @@
   // This is a function that will return a helper function that does the
   // iteration of the sync*.
   //
   // Each invocation should give a body with fresh state.
   final dynamic /* js function */ _outerHelper;
 
   SyncStarIterable(this._outerHelper);
 
   Iterator get iterator => new SyncStarIterator(JS('', '#()', _outerHelper));
 }