Refactor: Make MediaCaptureDevicesDispatcher have pluggable handlers.

chrome/browser/media/desktop_capture_access_handler.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.
+
+#ifndef CHROME_BROWSER_MEDIA_DESKTOP_CAPTURE_ACCESS_HANDLER_H_
+#define CHROME_BROWSER_MEDIA_DESKTOP_CAPTURE_ACCESS_HANDLER_H_
+
+#include "chrome/browser/media/media_access_handler.h"
+
+class DesktopStreamsRegistry;
+
+class DesktopCaptureAccessHandler : public MediaAccessHandler {
+ public:
+  DesktopCaptureAccessHandler();
+  ~DesktopCaptureAccessHandler() override;
+
+  // MediaAccessHandler implementation.
+  bool SupportsRequest(const content::MediaStreamRequest& request,
+                       const extensions::Extension* extension) override;
+  void HandleRequest(content::WebContents* web_contents,
+                     const content::MediaStreamRequest& request,
+                     const content::MediaResponseCallback& callback,
+                     const extensions::Extension* extension) override;
+
+ private:
+  void ProcessScreenCaptureAccessRequest(
+      content::WebContents* web_contents,
+      const content::MediaStreamRequest& request,
+      const content::MediaResponseCallback& callback,
+      const extensions::Extension* extension);
+};
+
+#endif  // CHROME_BROWSER_MEDIA_DESKTOP_CAPTURE_ACCESS_HANDLER_H_