Fix a crash in MimeHandlerServiceImpl::AbortStream().

extensions/browser/api/mime_handler_private/mime_handler_private.cc

 // Copyright 2015 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.
 
 #include "extensions/browser/api/mime_handler_private/mime_handler_private.h"
 
 #include "content/public/browser/stream_handle.h"
 #include "content/public/browser/stream_info.h"
 #include "extensions/browser/guest_view/mime_handler_view/mime_handler_view_guest.h"
 #include "extensions/common/constants.h"
@@ skipping 42 matching lines @@
     const mojo::Callback<void(mime_handler::StreamInfoPtr)>& callback) {
   if (!stream_) {
     callback.Run(mime_handler::StreamInfoPtr());
     return;
   }
   callback.Run(mojo::ConvertTo<mime_handler::StreamInfoPtr>(*stream_));
 }
 
 void MimeHandlerServiceImpl::AbortStream(
     const mojo::Callback<void()>& callback) {
+  if (!stream_) {
+    callback.Run();
+    return;
+  }
   stream_->Abort(base::Bind(&MimeHandlerServiceImpl::OnStreamClosed,
                             weak_factory_.GetWeakPtr(), callback));
 }
 
 void MimeHandlerServiceImpl::OnStreamClosed(
     const mojo::Callback<void()>& callback) {
   callback.Run();
 }
 
 }  // namespace extensions
@@ skipping 13 matching lines @@
   const content::StreamInfo* info = stream.stream_info();
   result->mime_type = info->mime_type;
   result->original_url = info->original_url.spec();
   result->stream_url = info->handle->GetURL().spec();
   result->response_headers =
       extensions::CreateResponseHeadersMap(info->response_headers.get());
   return result.Pass();
 }
 
 }  // namespace mojo