Preserve the stack trace for rethrown exceptions in Future.transformException.

tests/corelib/future_test.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.
 
 // Tests for Future.immediate
 
 testImmediate() {
   final future = new Future<String>.immediate("42");
   Expect.isTrue(future.isComplete);
   Expect.isTrue(future.hasValue);
@@ skipping 333 matching lines @@
   final completer = new Completer();
   final chained = completer.future.chain((_) {
     throw 'whoops!';
   });
 
   final stackTrace = 'fake stack trace';
   completer.complete('blah');
   Expect.isNotNull(chained.stackTrace);
 }
 
+testCallStackIsPreservedIfExceptionIsRethrownInTransformException() {
+  final completer = new Completer();
+  var chained = completer.future.chain((_) {
+    throw 'whoops!';
+  });
+  var transformed = chained.transformException((e) {
+    throw e;
+  });
+
+  completer.complete('blah');
+  Expect.equals(transformed.stackTrace, chained.stackTrace);
+}
+
 // Tests for mixed usage of [onComplete], [then], and [handleException]
 
 testCompleteWithCompletionAndSuccessHandlers() {
   final completer = new Completer<int>();
   final future = completer.future;
 
   var valueFromSuccessHandler;
   var valueFromCompletionHandler;
   future.onComplete((f) {
     Expect.isNotNull(valueFromSuccessHandler);
@@ skipping 306 matching lines @@
   testExceptionHandlerReturnsTrue2();
   testExceptionHandlerReturnsFalse();
   testExceptionHandlerReturnsFalse2();
   testExceptionHandlerAfterCompleteThenNotCalled();
   testExceptionHandlerAfterCompleteReturnsFalseThenThrows();
   testCallStackThrowsIfNotComplete();
   testCallStackIsNullIfCompletedSuccessfully();
   testCallStackReturnsCallstackPassedToCompleteException();
   testCallStackIsCapturedIfTransformCallbackThrows();
   testCallStackIsCapturedIfChainCallbackThrows();
+  testCallStackIsPreservedIfExceptionIsRethrownInTransformException();
   testCompleteWithCompletionAndSuccessHandlers();
   testExceptionWithCompletionAndSuccessHandlers();
   testExceptionWithCompletionAndSuccessAndExceptionHandlers();
   testTransformSuccess();
   testTransformFutureFails();
   testTransformTransformerFails();
   testChainSuccess();
   testChainFirstFutureFails();
   testChainTransformerFails();
   testChainSecondFutureFails();
   testTransformExceptionCompletesNormally();
   testTransformExceptionThrows();
   testTransformExceptionReturns();
   testTransformExceptionReturnsAFuture();
   testExceptionTravelsAlongBothBranches();
   testExceptionTravelsAlongBothBranchesAfterComplete();
   testExceptionIsHandledInBaseAndBranch();
   testExceptionIsHandledInBaseAndBranchAfterComplete();
 }