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

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

Index: chrome/browser/extensions/api/dial/device_description_fetcher.h
diff --git a/chrome/browser/extensions/api/dial/device_description_fetcher.h b/chrome/browser/extensions/api/dial/device_description_fetcher.h
index 309dc88a60007e340790bdd540412560125c73d2..12e8ee13ff2daaf1e1ed23ca70dc230b0ed2288b 100644
--- a/chrome/browser/extensions/api/dial/device_description_fetcher.h
+++ b/chrome/browser/extensions/api/dial/device_description_fetcher.h
@@ -9,13 +9,14 @@
 #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 {
@@ -27,17 +28,19 @@ 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);
 
@@ -60,7 +63,9 @@ class DeviceDescriptionFetcher : public net::URLFetcherDelegate {
   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_;