[Dial] Refactor DialRegistry and DeviceDescriptionFetcher so they can be used by MediaSinkService

chrome/browser/extensions/api/dial/device_description_fetcher.h

 // Copyright (c) 2017 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.
 
 #ifndef CHROME_BROWSER_EXTENSIONS_API_DIAL_DEVICE_DESCRIPTION_FETCHER_H_
 #define CHROME_BROWSER_EXTENSIONS_API_DIAL_DEVICE_DESCRIPTION_FETCHER_H_
 
 #include <memory>
 #include <string>
 
 #include "base/callback.h"
+#include "base/threading/thread_checker.h"
+#include "content/public/browser/browser_thread.h"
 #include "net/url_request/url_fetcher_delegate.h"
 #include "url/gurl.h"
 
-class Profile;
-
 namespace net {
 class URLFetcher;
+class URLRequestContextGetter;
 }
 
 namespace extensions {
 namespace api {
 namespace dial {
 
 struct DialDeviceDescriptionData;
 
 // Used to make a single HTTP GET request with |device_description_url| to fetch
 // a uPnP device description from a DIAL device.  If successful, |success_cb| is
 // invoked with the result; otherwise, |error_cb| is invoked with an error
-// reason.  This class is not thread safe and must be used on the UI thread.
+// reason.
+// This class is not thread safe.
 class DeviceDescriptionFetcher : public net::URLFetcherDelegate {
  public:
   // Used to identify the net::URLFetcher instance for tests.
   static constexpr int kURLFetcherIDForTest = 1;
 
-  // |profile| is unowned; the caller must ensure that this object does not
-  // outlive it.
+  // |request_context| is unowned; the caller must ensure that this object does
+  // not outlive it.
   DeviceDescriptionFetcher(
       const GURL& device_description_url,
-      Profile* profile,
+      net::URLRequestContextGetter* request_context,

[imcheng, 2017/03/06 20:56:30]

I believe this should be a scoped_refptr; this object is passed from UI thread
to IO thread. URLRequestContextGetter inherits RefCountedThreadSafe.

[zhaobin, 2017/03/07 00:13:18]

Pass in raw pointer (Profile::GetRequestContext() returns raw pointer) and store
it as scoped_refptr?

[imcheng, 2017/03/07 20:32:58]

Most likely you will pass in a scoped_refptr here, but not a big deal until you
start to use this on the IO thread. The reason is that if this object is created
on the IO thread, then you would need to pass in a net::URLRequestContextGetter
from the UI thread first. This means it should already be wrapped in a
scoped_refptr when posting the task, since you can't pass in a raw pointer to a
ref counted type  as a function argument in base::Bind.

More info here:
https://www.chromium.org/developers/coding-style/important-abstractions-and-d...

+      content::BrowserThread::ID thread_id,
       base::OnceCallback<void(const DialDeviceDescriptionData&)> success_cb,
       base::OnceCallback<void(const std::string&)> error_cb);
 
   ~DeviceDescriptionFetcher() override;
 
   void Start();
 
  private:
   // net::URLFetcherDelegate implementation.
   void OnURLFetchComplete(const net::URLFetcher* source) override;
   void OnURLFetchDownloadProgress(const net::URLFetcher* source,
                                   int64_t current,
                                   int64_t total,
                                   int64_t current_network_bytes) override;
   void OnURLFetchUploadProgress(const net::URLFetcher* source,
                                 int64_t current,
                                 int64_t total) override;
 
   // Runs |error_cb_| with |message| and clears it.
   void ReportError(const std::string& message);
 
   const GURL device_description_url_;
-  Profile* const profile_;
+  net::URLRequestContextGetter* const request_context_;
+  base::ThreadChecker thread_checker_;
+
   base::OnceCallback<void(const DialDeviceDescriptionData&)> success_cb_;
   base::OnceCallback<void(const std::string&)> error_cb_;
   std::unique_ptr<net::URLFetcher> fetcher_;
 };
 
 }  // namespace dial
 }  // namespace api
 }  // namespace extensions
 
 #endif  // CHROME_BROWSER_EXTENSIONS_API_DIAL_DEVICE_DESCRIPTION_FETCHER_H_