[DIAL] Break circular dependency in DialFetchDeviceDescriptionFunction.

chrome/browser/extensions/api/dial/dial_api.cc

 // 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.
 
 #include "chrome/browser/extensions/api/dial/dial_api.h"
 
 #include <stddef.h>
 #include <utility>
 #include <vector>
 
@@ skipping 220 matching lines @@
 
   device_description_fetcher_ = base::MakeUnique<DeviceDescriptionFetcher>(
       url, Profile::FromBrowserContext(browser_context()),
       base::BindOnce(&DialFetchDeviceDescriptionFunction::OnFetchComplete,
                      this),
       base::BindOnce(&DialFetchDeviceDescriptionFunction::OnFetchError, this));
 
   device_description_fetcher_->Start();
 }
 
 void DialFetchDeviceDescriptionFunction::OnFetchComplete(

[mark a. foltz, 2017/02/02 20:27:32]

Can you add a comment in device_description_fetcher.h indicating that it should
be destroyed in the onsuccess/onerror callbacks?

[imcheng, 2017/02/02 20:44:31]

I added comment here explaining why we have to destroy it here. It's due to the
way we bind the callbacks passed in.

     const api::dial::DialDeviceDescriptionData& result) {
+  device_description_fetcher_.reset();

[mark a. foltz, 2017/02/02 20:27:32]

Would resetting the non-invoked callback in DeviceDescriptionFetcher also fix
the problem by dropping the additional reference?  That wouldn't require the
client to drop references explicitly.

[imcheng, 2017/02/02 20:44:31]

Yes, that would work too. But I see no reason to hold on to the fetcher since
it's no longer (re)usable.

   api::dial::DialDeviceDescription device_description;
   device_description.device_label = params_->device_label;
   device_description.app_url = result.app_url.spec();
   device_description.device_description = result.device_description;
   SetResult(device_description.ToValue());
   SendResponse(true);
 }
 
 void DialFetchDeviceDescriptionFunction::OnFetchError(
     const std::string& message) {
+  device_description_fetcher_.reset();
   SetError(message);
   SendResponse(false);
 }
 
 }  // namespace extensions