Tab Audio Mirroring: WebContentsAudioInputStream is a new implementation which represents the lifet…

content/browser/renderer_host/media/web_contents_capture_util.h

Index: content/browser/renderer_host/media/web_contents_capture_util.h
diff --git a/content/browser/renderer_host/media/web_contents_capture_util.h b/content/browser/renderer_host/media/web_contents_capture_util.h
index 0256a5cd570d9fa1bf672e82fbfbb117fd551213..a577e84ab186384cdf1bd211cf67a0c2bc6341c1 100644
--- a/content/browser/renderer_host/media/web_contents_capture_util.h
+++ b/content/browser/renderer_host/media/web_contents_capture_util.h
@@ -7,6 +7,15 @@
 
 #include <string>
 
+#include "base/callback.h"
+#include "base/memory/ref_counted.h"
+#include "content/common/content_export.h"
+#include "content/public/browser/web_contents_observer.h"
+
+namespace base {
+class MessageLoopProxy;
+}
+
 namespace content {
 
 class WebContentsCaptureUtil {
@@ -28,6 +37,67 @@ class WebContentsCaptureUtil {
                                       int* render_view_id);
 };
 
+// Given a starting render_process_id and render_view_id, tracks RenderView
+// instance swapping during the lifetime of a WebContents instance.
+//
+// Threading issues: Start(), Stop() and the ChangeCallback are invoked on the
+// same thread.  This can be any thread, and the decision is locked-in by
+// WebContentsTracker when Start() is called.
+class CONTENT_EXPORT WebContentsTracker

[DaleCurtis, 2013/01/15 22:02:18]

Why put this here vs separate file vs private class in
WebContentsAudioInputStream? There's no coupling between WebContentsCaptureUtil
and this class.

[miu, 2013/01/16 03:22:18]

This class is a utility meant to be used by only WebContentsAudioInputStream and
WebContentsVideoCaptureDevice.  I was thinking it'd be good to keep such code
within the same module.  They're both related in that they're both used to find
and follow a RenderView by its IDs.

One option I had considered was to make it an inner class of
WebContentsCaptureUtil.  What do you think?

In a later CL, I'll change WebContentsVideoCaptureDevice to use this.  That way,
both audio and video capture will be tracking tab navigation exactly the same
way.

[DaleCurtis, 2013/01/17 01:15:52]

Hmm, it depends on the usage pattern. In general, utility classes indicate
things could be better organized. If both classes are going to use this, I'd
just as soon see it as a standalone class.

[miu, 2013/01/17 05:33:55]

Agreed.  This stuff with the device_id parsing is an interim solution until the
MediaStream messaging/factoring is worked out.  xians@ is in the middle of some
of this work, IIRC.

So, I took your comment to mean that you'd prefer this class to be in its own
.h/.cc files.  Done.

+    : public base::RefCountedThreadSafe<WebContentsTracker>,
+      public WebContentsObserver {
+ public:
+  WebContentsTracker();
+
+  // Callback for whenever the target is swapped.  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.  The callback will be invoked on the same thread calling Start().
+  virtual 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.
+  virtual void Stop();
+
+ protected:
+  friend class base::RefCountedThreadSafe<WebContentsTracker>;
+  virtual ~WebContentsTracker();
+
+ private:
+  // Reads the render_process_id/render_view_id from the current WebContents
+  // instance and then invokes the callback.
+  void OnWebContentsChangeEvent();
+
+  // Called on the thread that Start()/Stop() are called on, check whether the
+  // callback is still valid and, if so, invoke it.
+  void MaybeDoCallback(int render_process_id, int render_view_id);
+
+  // 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);
+
+  // WebContentsObserver overrides to react to events of interest.
+  virtual void RenderViewReady() OVERRIDE;
+  virtual void AboutToNavigateRenderView(RenderViewHost* render_view_host)
+      OVERRIDE;
+  virtual void DidNavigateMainFrame(const LoadCommittedDetails& details,
+                                    const FrameNavigateParams& params) OVERRIDE;
+  virtual void WebContentsDestroyed(WebContents* web_contents) OVERRIDE;
+
+  scoped_refptr<base::MessageLoopProxy> message_loop_;
+  ChangeCallback callback_;
+
+  DISALLOW_COPY_AND_ASSIGN(WebContentsTracker);
+};
+
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_RENDERER_HOST_MEDIA_WEB_CONTENTS_CAPTURE_UTIL_H_