Fix dart2js async error handling of finallies nested in finallies.

tests/language/async_throw_in_catch_test.dart

 // Copyright (c) 2015, 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.
 
 import "dart:async";
 import "package:expect/expect.dart";
 import "package:async_helper/async_helper.dart";
 
 class Tracer {
   final String expected;
@@ skipping 386 matching lines @@
       throw "Error3";
     } finally {
       tracer.trace("f");
     }
   } finally {
     tracer.trace("g");
   }
   tracer.trace("h");
 }
 
+foo17(Tracer tracer) async {
+  try {
+    tracer.trace("a");
+  } finally {
+    try {
+      tracer.trace("b");
+      throw "Error";
+    } catch (error) {
+      await new Future.value(3);  /// forceAwait: continued
+      Expect.equals("Error", error);
+      tracer.trace("c");
+    } finally {
+      tracer.trace("d");
+    }
+    tracer.trace("e");
+  }
+  tracer.trace("f");
+}
+
+foo18(Tracer tracer) async {
+  try {
+      tracer.trace("a");
+  } finally {
+    try {
+      tracer.trace("b");
+    } finally {
+      await new Future.value(3);  /// forceAwait: continued
+      tracer.trace("c");
+    }
+    tracer.trace("d");
+  }
+  tracer.trace("e");
+}
+
 runTest(expectedTrace, fun, [expectedError]) async {
   Tracer tracer = new Tracer(expectedTrace);
   try {
     await fun(tracer);
   } catch (error) {
     Expect.equals(expectedError, error);
     tracer.trace("X");
   }
   tracer.done();
 }
 
 test() async {
   await runTest("abceX", foo1, "Error2");
   await runTest("abdeX", foo2, "Error2");
   await runTest("abde", foo3);
   await runTest("abcd", foo4);
   await runTest("abcdX", foo5, "Error2");
   await runTest("abcde", foo6);
   await runTest("abcdX", foo7, "Error3");
   await runTest("abcdX", foo8, "Error3");
   await runTest("abcef", foo9);
   await runTest("abcdefgabcdefghi", foo10);
   await runTest("abcdaef", foo11);
   await runTest("abcdfg", foo12);
   await runTest("acdefgX", foo13, "Error");
   await runTest("abcdefgX", foo14, "Error3");
   await runTest("abcdefgX", foo14, "Error3");
   await runTest("abcdefg", foo15);
   await runTest("abcdfg", foo16);
+  await runTest("abcdef", foo17);
+  await runTest("abcde", foo18);
 }
 
 void main() {
   asyncTest(test);
 }