Fix a FileWriter abort race by turning an assert into a soft check.

See https://bugs.webkit.org/show_bug.cgi?id=81861 for the other side of this.

BUG=119417
TEST=existing tests get less flaky

Review URL: http://codereview.chromium.org/9764018

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@129488 0039d316-1c4b-4281-b951-d872f2087c98

webkit/fileapi/webfilewriter_base.cc

-// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
@@ -54,7 +54,9 @@ void WebFileWriterBase::write(
 // thing to come back is the cancel response.  We only notify the
 // AsyncFileWriterClient when it's all over.
 void WebFileWriterBase::cancel() {
-  DCHECK(kOperationWrite == operation_ || kOperationTruncate == operation_);
+  // Check for the cancel passing the previous operation's return in-flight.
+  if (kOperationWrite != operation_ && kOperationTruncate != operation_)
+    return;
   if (kCancelNotInProgress != cancel_state_)
     return;
   cancel_state_ = kCancelSent;