WebLayer: fix crash in MediaStreamUi

If the MediaStreamManager were destroyed after a MediaStreamUi was
created but before it started recording, it wouldn't call OnManagerGone
on the MediaStreamUi.

Switch to using a WeakPtr.

Bug: 1147646
Change-Id: I72010ed73daa26c4f682e2779efe046d1ddb2020
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2532966Reviewed-by: Clark DuVall <cduvall@chromium.org>
Commit-Queue: Evan Stade <estade@chromium.org>
Cr-Commit-Position: refs/heads/master@{#826454}

weblayer/browser/webrtc/media_stream_manager.cc

@@ -41,7 +41,7 @@ void FindStreamTypes(const blink::MediaStreamDevices& devices,
 // is passed off to MediaResponseCallback.
 class MediaStreamManager::StreamUi : public content::MediaStreamUI {
  public:
-  StreamUi(MediaStreamManager* manager,
+  StreamUi(base::WeakPtr<MediaStreamManager> manager,
            const blink::MediaStreamDevices& devices)
       : manager_(manager) {
     DCHECK(manager_);
@@ -70,8 +70,6 @@ class MediaStreamManager::StreamUi : public content::MediaStreamUI {
   void OnDeviceStopped(const std::string& label,
                        const content::DesktopMediaID& media_id) override {}
 
-  void OnManagerGone() { manager_ = nullptr; }
-
   bool streaming_audio() const { return streaming_audio_; }
 
   bool streaming_video() const { return streaming_video_; }
@@ -79,7 +77,7 @@ class MediaStreamManager::StreamUi : public content::MediaStreamUI {
   void Stop() { std::move(stop_).Run(); }
 
  private:
-  MediaStreamManager* manager_;
+  base::WeakPtr<MediaStreamManager> manager_;
   bool streaming_audio_ = false;
   bool streaming_video_ = false;
   base::OnceClosure stop_;
@@ -95,10 +93,7 @@ MediaStreamManager::MediaStreamManager(
       ->SetUserData(&kWebContentsUserDataKey, std::move(user_data));
 }
 
-MediaStreamManager::~MediaStreamManager() {
-  for (auto* stream : active_streams_)
-    stream->OnManagerGone();
-}
+MediaStreamManager::~MediaStreamManager() = default;
 
 // static
 MediaStreamManager* MediaStreamManager::FromWebContents(
@@ -127,7 +122,8 @@ void MediaStreamManager::OnClientReadyToStream(JNIEnv* env,
   if (allowed) {
     std::move(request->second.callback)
         .Run(request->second.devices, request->second.result,
-             std::make_unique<StreamUi>(this, request->second.devices));
+             std::make_unique<StreamUi>(weak_factory_.GetWeakPtr(),
+                                        request->second.devices));
   } else {
     std::move(request->second.callback)
         .Run({}, blink::mojom::MediaStreamRequestResult::NO_HARDWARE, {});