media: Simplify MediaPermissionDispatcher.

content/renderer/media/media_permission_dispatcher.h

 // 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.
 
-// Base class for MediaPermission implementations in content. This class allows
-// multiple pending PermissionService calls by managing callbacks for its
-// subclasses. This class is not thread safe and should only be used on one
-// thread.
-
 #ifndef CONTENT_RENDERER_MEDIA_MEDIA_PERMISSION_DISPATCHER_H_
 #define CONTENT_RENDERER_MEDIA_MEDIA_PERMISSION_DISPATCHER_H_
 
 #include <stdint.h>
 
 #include <map>
 
 #include "base/macros.h"
+#include "base/memory/ref_counted.h"
 #include "base/memory/weak_ptr.h"
-#include "base/threading/thread_checker.h"
 #include "content/common/content_export.h"
+#include "content/common/permission_service.mojom.h"
+#include "content/public/renderer/render_frame_observer.h"
 #include "media/base/media_permission.h"
 
+namespace base {
+class SingleThreadTaskRunner;
+}
+
 namespace content {
 
-class CONTENT_EXPORT MediaPermissionDispatcher : public media::MediaPermission {
+// MediaPermission implementation.
+class CONTENT_EXPORT MediaPermissionDispatcher : public media::MediaPermission,
+                                                 public RenderFrameObserver {
  public:
-  MediaPermissionDispatcher();
+  explicit MediaPermissionDispatcher(RenderFrame* render_frame);
   ~MediaPermissionDispatcher() override;
 
- protected:
-  // Register callbacks for PermissionService calls.
-  uint32_t RegisterCallback(const PermissionStatusCB& permission_status_cb);
-
-  // Deliver the permission status |granted| to the callback identified by
-  // |request_id|.
-  void DeliverResult(uint32_t request_id, bool granted);
-
-  base::ThreadChecker& thread_checker() { return thread_checker_; }
+  // media::MediaPermission implementation.
+  // Note: Can be called on any thread but the caller needs to make sure |this|

[perkj_chrome, 2016/01/25 21:19:56]

 |this| must be valid? Yes - it is a public method. I am afraid I dont
understand what you mean.

[xhwang, 2016/01/29 01:01:56]

Good point :) Since we are passing a raw pointer to MediaPermissionDispatcher
(hence |this|) around, the caller needs to make sure the raw pointer is still
valid at the time of the call. Otherwise it'll crash.

But I agree with you this seems dumb and confusing.

Updated.

+  // is valid at the time of this call. The |permission_status_cb| will always
+  // be fired on the thread where these methods are called.
+  void HasPermission(Type type,
+                     const GURL& security_origin,
+                     const PermissionStatusCB& permission_status_cb) override;
+  void RequestPermission(
+      Type type,
+      const GURL& security_origin,
+      const PermissionStatusCB& permission_status_cb) override;
 
  private:
   // Map of request IDs and pending PermissionStatusCBs.
   typedef std::map<uint32_t, PermissionStatusCB> RequestMap;
 
-  base::ThreadChecker thread_checker_;
+  // Register PermissionStatusCBs. Returns |request_id| that can be used to make
+  // PermissionService calls.
+  uint32_t RegisterCallback(const PermissionStatusCB& permission_status_cb);
 
+  // Callback for |permission_service_| calls.
+  void OnPermissionStatus(uint32_t request_id, PermissionStatus status);
+
+  scoped_refptr<base::SingleThreadTaskRunner> task_runner_;
   uint32_t next_request_id_;
   RequestMap requests_;
+  PermissionServicePtr permission_service_;
+
+  // Used to safely post MediaPermission calls for execution on |task_runner_|.
+  base::WeakPtr<MediaPermissionDispatcher> weak_ptr_;
+
+  base::WeakPtrFactory<MediaPermissionDispatcher> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(MediaPermissionDispatcher);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_RENDERER_MEDIA_MEDIA_PERMISSION_DISPATCHER_H_