Tab Audio Capture: Browser-side connect/disconnect functionality.

content/browser/renderer_host/media/web_contents_capture_util.h

 // Copyright (c) 2012 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 CONTENT_BROWSER_RENDERER_HOST_MEDIA_WEB_CONTENTS_CAPTURE_UTIL_H_
 #define CONTENT_BROWSER_RENDERER_HOST_MEDIA_WEB_CONTENTS_CAPTURE_UTIL_H_
 
 #include <string>
 
+#include "base/callback.h"
+#include "base/memory/ref_counted.h"
+#include "base/synchronization/lock.h"
+#include "content/public/browser/web_contents_observer.h"
+
 namespace content {
 
 class WebContentsCaptureUtil {
  public:
+  // Tracks RenderView changes during the lifetime of a WebContents instance.
+  //
+  // Thread-safety: Since the RenderViewTracker is intended to be used by both
+  // WebContentsAudioInputStream and WebContentsVideoCaptureDevice, it operates
+  // under the assumption that any thread could call the Start/Stop methods.
+  // Likewise, while the ChangeCallback is invoked from the UI BrowserThread, it
+  // is up to downstream code to trampoline to some other thread if necessary.
+  class RenderViewTracker
+      : public base::RefCountedThreadSafe<RenderViewTracker>,
+        public WebContentsObserver {
+   public:
+    RenderViewTracker();
+
+    // Callback for whenever a new RenderView is swapped in.  The callback is
+    // also invoked with both arguments set to MSG_ROUTING_NONE to indicate
+    // tracking will not continue (i.e., the WebContents instance was not found
+    // or has been destroyed).
+    typedef base::Callback<void(int render_process_id, int render_view_id)>
+        ChangeCallback;
+
+    // Start tracking.  The last-known |render_process_id| and |render_view_id|
+    // are provided, and the given callback is invoked asynchronously one or
+    // more times.
+    void Start(int render_process_id, int render_view_id,
+               const ChangeCallback& callback);
+
+    // Stop tracking.  Once this method returns, the callback is guaranteed not
+    // to be invoked again.
+    void Stop();
+
+   private:
+    friend class base::RefCountedThreadSafe<RenderViewTracker>;
+
+    virtual ~RenderViewTracker();
+
+    // Reads the render_process_id/render_view_id from the current WebContents
+    // instance and then invokes the callback.
+    void OnWebContentsChangeEvent();
+
+    // Look-up the current WebContents instance associated with the given
+    // |render_process_id| and |render_view_id| and begin observing it.
+    void LookUpAndObserveWebContents(int render_process_id,
+                                     int render_view_id);
+
+    // How WebContents notifies us of a new RenderView target.
+    virtual void RenderViewReady() OVERRIDE;
+
+    // Called when a WebContents has been destroyed.  This invokes the callback
+    // with MSG_ROUTING_NONE values to indicate tracking will not continue.
+    virtual void WebContentsDestroyed(WebContents* web_contents) OVERRIDE;
+
+    base::Lock lock_;  // Guards changes to callback_.
+    ChangeCallback callback_;
+  };
+
   // Function to extract the target renderer id's from a tab media stream
   // request's device id.
   static bool ExtractTabCaptureTarget(const std::string& device_id,
                                       int* render_process_id,
                                       int* render_view_id);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_RENDERER_HOST_MEDIA_WEB_CONTENTS_CAPTURE_UTIL_H_