[Docs] Updates media/capture docs: Debug logs for WebRTC Web APIs

Change-Id: Ia5fb0186b4ebe0624838a06bd3f8a4ccbbdb4534
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4790361
Reviewed-by: Mark Foltz <mfoltz@chromium.org>
Commit-Queue: Henrik Andreasson <henrika@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1185115}

docs/media/capture/README.md

@@ -155,29 +155,75 @@ Allows the user to switch the camera/microphone used for capture via an icon in
 
 # APIs
 
-## getUserMedia()
+## [getUserMedia()](https://rawgit.com/w3c/mediacapture-main/master/getusermedia.html)
 
 Web API for Web applications to capture camera and microphone input.
 
 * Code
   * `//third_party/blink/renderer/modules/mediastream/`
+  * `//third_party/blink/renderer/platform/webrtc/`
 * Issues
-  * `Blink>GetUserMedia`
+  * [`Blink>GetUserMedia`](https://bugs.chromium.org/p/chromium/issues/list?q=component%3ABlink%3EGetUserMedia&can=2)
 * Docs
   * To be added later.
 
-
-## getDisplayMedia()
+## [getDisplayMedia()](https://w3c.github.io/mediacapture-screen-share/)
 
 Web API for Web applications to capture screen contents and system/tab audio.
 
 * Code
   * `//third_party/blink/renderer/modules/mediastream/`
 * Issues
-  * `Blink>GetDisplayMedia`
+  * [`Blink>GetDisplayMedia`](https://bugs.chromium.org/p/chromium/issues/list?q=component%3ABlink%3EGetDisplayMedia&can=2)
 * Docs
   * To be added later.
 
+# Logs
+
+Usage of the APIs above involves several media layers in Chrome and can contain
+both audio and video streams. Logs from the most essential classes are
+centralized and all pass through:
+* [`content/browser/renderer_host/media/media_stream_manager.cc`](https://source.chromium.org/chromium/chromium/src/+/main:content/browser/renderer_host/media/media_stream_manager.cc), and
+* [`third_party/blink/renderer/platform/webrtc/webrtc_logging.cc`](https://source.chromium.org/chromium/chromium/src/+/main:third_party/blink/renderer/platform/webrtc/webrtc_logging.cc)
+
+It is possible to view these logs by adding special log filters (using a local
+Chromium build in this example):
+```
+./out/Default/chrome --enable-logging --vmodule=*/content/browser/renderer_host/media/*=1,*/third_party/blink/renderer/platform/webrtc/*=1
+```
+
+Each log line is prepended with a tag corresponding to an abbreviation of the
+class which generated the log. E.g. `UMP::` for `UserMediaProcessor`, `PLAS::`
+for `ProcessedLocalAudioSource`, `AIC::` for `AudioInputController`, `AMB::` for
+`AudioManagerBase` etc. The tags enable post processing of the captured logs to
+analyze how a web client uses specified classes or modules in Chrome.
+
+The example below is from a [WebRTC demo client](https://webrtc.github.io/samples/src/content/getusermedia/audio/) which uses `getUserMedia` to captures audio and then render it locally:
+
+```
+less ./out/Default/chrome_debug.log | grep 'UMP'
+
+[11460:25180:0817/133550.056:VERBOSE1:webrtc_logging.cc(35)] UMP::ProcessRequest({request_id=0}, {audio=1}, {video=0})
+[11460:25180:0817/133550.056:VERBOSE1:webrtc_logging.cc(35)] UMP::SetupAudioInput({request_id=0}, {constraints=})
+[11460:25180:0817/133550.056:VERBOSE1:webrtc_logging.cc(35)] UMP::SetupAudioInput({request_id=0}) => (Requesting device capabilities)
+[11460:25180:0817/133550.843:VERBOSE1:webrtc_logging.cc(35)] UMP::SelectAudioSettings({request_id=0})
+[11460:25180:0817/133550.853:VERBOSE1:webrtc_logging.cc(35)] UMP::GenerateStreamForCurrentRequestInfo({request_id=0}, {audio.device_id=default}, {video.device_id=})
+[11460:25180:0817/133550.911:VERBOSE1:webrtc_logging.cc(35)] UMP::OnStreamsGenerated({request_id=0}, {label=b24a1017-a129-4465-b1fa-f4d9c553d956}, {device=[id: default, name: Default - Microphone (Realtek(R) Audio)]})
+[11460:25180:0817/133550.911:VERBOSE1:webrtc_logging.cc(35)] UMP::StartTracks({request_id=0}, {label=b24a1017-a129-4465-b1fa-f4d9c553d956})
+[11460:25180:0817/133550.913:VERBOSE1:webrtc_logging.cc(35)] UMP::CreateAudioTrack({render_to_associated_sink=0})
+[11460:25180:0817/133550.913:VERBOSE1:webrtc_logging.cc(35)] UMP::InitializeAudioSourceObject({session_id=4FF8214D8180F02B8A9206564C59C03D})
+[11460:25180:0817/133550.914:VERBOSE1:webrtc_logging.cc(35)] UMP::CreateAudioSource => (audiprocessing is required)
+[11460:25180:0817/133550.922:VERBOSE1:webrtc_logging.cc(35)] UMP::StartAudioTrack({track=[id: 9803bb62-5cdc-4279-b58e-fd1193d7ecd8, enabled: 1]}, {is_pending=1})
+[11460:25180:0817/133550.922:VERBOSE1:webrtc_logging.cc(35)] UMP::StartAudioTrack(source: {session_id=4FF8214D8180F02B8A9206564C59C03D}, {is_local_source=1}, {device=[id: default, group_id: def1842e91c7bc3d9c2be5618262afa5413975edb13d4a33c266224daed0a478, name: Default - Microphone (Realtek(R) Audio)]})
+[11460:25180:0817/133551.330:VERBOSE1:webrtc_logging.cc(35)] UMP::OnTrackStarted({session_id=4FF8214D8180F02B8A9206564C59C03D}, {result=OK})
+[11460:25180:0817/133551.330:VERBOSE1:webrtc_logging.cc(35)] UMP::UMP::OnCreateNativeTracksCompleted({request_id=0}, {label=b24a1017-a129-4465-b1fa-f4d9c553d956})
+[11460:25180:0817/133551.330:VERBOSE1:webrtc_logging.cc(35)] UMP::GetUserMediaRequestSucceeded({request_id=0})
+[11460:25180:0817/133551.331:VERBOSE1:webrtc_logging.cc(35)] UMP::DelayedGetUserMediaRequestSucceeded({request_id=0}, {result=OK})
+[11460:25180:0817/133553.114:VERBOSE1:webrtc_logging.cc(35)] UMP::OnDeviceStopped({session_id=4FF8214D8180F02B8A9206564C59C03D}, {device_id=default})
+[11460:25180:0817/133553.115:VERBOSE1:webrtc_logging.cc(35)] UMP::StopLocalSource({session_id=4FF8214D8180F02B8A9206564C59C03D})
+[11460:25180:0817/133553.123:VERBOSE1:webrtc_logging.cc(35)] UMP::RemoveLocalSource({id=default}, {name=Default - Microphone (Realtek(R) Audio)}, {group_id=def1842e91c7bc3d9c2be5618262afa5413975edb13d4a33c266224daed0a478})
+```
+
 # Additional features
 
 Not all media capture features are listed above; here are some additional