Video Capture: Allow suspension of individual devices.

content/renderer/media/media_stream_video_capturer_source.cc

Index: content/renderer/media/media_stream_video_capturer_source.cc
diff --git a/content/renderer/media/media_stream_video_capturer_source.cc b/content/renderer/media/media_stream_video_capturer_source.cc
index 15583dcfc7438eec5444d90885453ab603a86a2f..ab890fc062627553b1dec9d1219975532304c912 100644
--- a/content/renderer/media/media_stream_video_capturer_source.cc
+++ b/content/renderer/media/media_stream_video_capturer_source.cc
@@ -8,6 +8,7 @@
 
 #include "base/bind.h"
 #include "base/callback_helpers.h"
+#include "base/debug/stack_trace.h"
 #include "base/location.h"
 #include "base/macros.h"
 #include "base/strings/utf_string_conversions.h"
@@ -212,6 +213,8 @@ class LocalVideoCapturerSource final : public media::VideoCapturerSource {
                     const VideoCaptureDeliverFrameCB& new_frame_callback,
                     const RunningCallback& running_callback) override;
   void RequestRefreshFrame() override;
+  void MaybeSuspend() override;
+  void Resume() override;
   void StopCapture() override;
 
  private:
@@ -230,10 +233,13 @@ class LocalVideoCapturerSource final : public media::VideoCapturerSource {
   // Indicates if we are capturing generated content, e.g. Tab or Desktop.
   const bool is_content_capture_;
 
-  // These two are valid between StartCapture() and StopCapture().
-  base::Closure stop_capture_cb_;
+  // This is run once to report whether the device was successfully started
+  // after a call to StartCapture().
   RunningCallback running_callback_;
 
+  // This is valid between StartCapture() and StopCapture().
+  base::Closure stop_capture_cb_;
+
   // Placeholder keeping the callback between asynchronous device enumeration
   // calls.
   VideoCaptureDeviceFormatsCB formats_enumerated_callback_;
@@ -319,6 +325,18 @@ void LocalVideoCapturerSource::RequestRefreshFrame() {
   manager_->RequestRefreshFrame(session_id_);
 }
 
+void LocalVideoCapturerSource::MaybeSuspend() {
+  DVLOG(3) << __func__;
+  DCHECK(thread_checker_.CalledOnValidThread());
+  manager_->Suspend(session_id_);
+}
+
+void LocalVideoCapturerSource::Resume() {
+  DVLOG(3) << __func__;
+  DCHECK(thread_checker_.CalledOnValidThread());
+  manager_->Resume(session_id_);
+}
+
 void LocalVideoCapturerSource::StopCapture() {
   DVLOG(3) << __func__;
   DCHECK(thread_checker_.CalledOnValidThread());
@@ -335,10 +353,24 @@ void LocalVideoCapturerSource::OnStateUpdate(VideoCaptureState state) {
   DCHECK(thread_checker_.CalledOnValidThread());
   if (running_callback_.is_null())
     return;
-  const bool is_started_ok = state == VIDEO_CAPTURE_STATE_STARTED;
-  running_callback_.Run(is_started_ok);
-  if (!is_started_ok)
-    running_callback_.Reset();
+  switch (state) {
+    case VIDEO_CAPTURE_STATE_STARTED:
+      base::ResetAndReturn(&running_callback_).Run(true);
+      break;
+
+    case VIDEO_CAPTURE_STATE_STOPPING:
+    case VIDEO_CAPTURE_STATE_STOPPED:
+    case VIDEO_CAPTURE_STATE_ERROR:
+    case VIDEO_CAPTURE_STATE_ENDED:
+      base::ResetAndReturn(&running_callback_).Run(false);
+      break;
+
+    case VIDEO_CAPTURE_STATE_STARTING:
+    case VIDEO_CAPTURE_STATE_PAUSED:
+    case VIDEO_CAPTURE_STATE_RESUMED:
+      // Not applicable to reporting on device start success/failure.
+      break;
+  }

[chfremer, 2016/09/27 00:54:59]

I see a slight change of behavior here. Before, device start was reported as
failure in more of the cases. 
Did it actually happen that one of these states were called before one of the
others and was this a bug?
Or is this change just to handle it "more correctly" in case of future changes?

Are there any tests for this?

[miu, 2016/09/27 23:42:23]

The purpose of this function was to report on whether the start succeeded
(because running_callback_ calls MediaStreamVideoSource::OnStartDone()). So,
yes, the prior implementation was wrong.

I realized it was wrong when I added the VIDEO_CAPTURE_STATE_PAUSED/RESUMED
status updates from the VideoCaptureHost, and this was calling OnStartDone()
multiple times.
Not that I can tell. However, all the MediaStream-related stuff is covered in
layout tests. Also, my follow-up change requires this to work correctly (and
provides test coverage in the tab capture end-to-end browser tests).

 }
 
 void LocalVideoCapturerSource::OnDeviceFormatsInUseReceived(
@@ -414,6 +446,13 @@ void MediaStreamVideoCapturerSource::RequestRefreshFrame() {
   source_->RequestRefreshFrame();
 }
 
+void MediaStreamVideoCapturerSource::SetHasConsumers(bool has_consumers) {
+  if (has_consumers)
+    source_->Resume();
+  else
+    source_->MaybeSuspend();
+}
+
 void MediaStreamVideoCapturerSource::SetCapturingLinkSecured(bool is_secure) {
   Send(new MediaStreamHostMsg_SetCapturingLinkSecured(
       device_info().session_id, device_info().device.type, is_secure));