[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 "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 and must be used on the UI or IO thread.

[mark a. foltz, 2017/03/01 21:44:00]

It's safe to use the URLFetcher from either thread, so this class should also be
safe.  However the public API must use the thread checker to prevent
cross-thread usage.

Nit: I would just leave the comment above as "not thread safe" 

[zhaobin, 2017/03/02 07:04:35]

Done.

 class DeviceDescriptionFetcher : public net::URLFetcherDelegate {

[imcheng, 2017/02/22 03:45:04]

I would make it clear that an instance must only be used exclusively on the UI
thread or exclusively on the IO thread (e.g., you can't create it on UI thread
then call Start() on IO thread). On the other hand, I feel it would it simpler
if we only allowed this from the IO thread, as that means fewer thread hops for
both DialMediaSinkService and dial.fetchDeviceDescription implementation. The
net::URLRequestContextGetter itself is RefCountedThreadSafe which means you can
pass it from UI to IO thread. Mark, WDYT?

[zhaobin, 2017/03/02 07:04:35]

Acknowledged.

  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,
+      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_;
+  content::BrowserThread::ID thread_id_;
+
   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_