Let Flash join and be controlled by media session

content/browser/media/session/pepper_playback_observer.cc

+// Copyright 2016 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.
+
+#include "content/browser/media/session/pepper_playback_observer.h"
+
+#include "base/feature_list.h"
+#include "content/browser/media/session/media_session.h"
+#include "content/browser/media/session/pepper_player_delegate.h"
+#include "content/common/frame_messages.h"
+#include "ipc/ipc_message_macros.h"
+#include "media/base/media_switches.h"
+
+namespace content {
+
+PepperPlaybackObserver::PepperPlaybackObserver(WebContents *contents)
+    : contents_(contents) {}
+
+PepperPlaybackObserver::~PepperPlaybackObserver() {
+  // At this point WebContents is being destructed, so it's safe to
+  // call this. MediaSession may decide to send further IPC messages
+  // through PepperPlayerDelegates, which might be declined if the
+  // RenderViewHost has been destroyed.
+  for (PlayersMap::iterator iter(&players_map_);
+       !iter.IsAtEnd(); iter.Advance())
+    PepperStopsPlayback(iter.GetCurrentKey());

[mlamouri (slow - plz ping), 2016/06/30 11:01:18]

style: can you wrap this into { }

[Zhiqiang Zhang (Slow), 2016/06/30 12:46:54]

Done.

+  contents_ = nullptr;
+}
+
+void PepperPlaybackObserver::PepperInstanceCreated(int32_t pp_instance) {
+}
+
+void PepperPlaybackObserver::PepperInstanceDeleted(int32_t pp_instance) {
+  PepperStopsPlayback(pp_instance);
+}
+
+void PepperPlaybackObserver::PepperStartsPlayback(int32_t pp_instance) {
+  if (!base::FeatureList::IsEnabled(media::kFlashJoinsMediaSession))
+    return;
+
+  if (players_map_.Lookup(pp_instance))
+    return;
+
+  players_map_.AddWithID(new PepperPlayerDelegate(

[dcheng, 2016/06/30 07:02:39]

Would an ordinary std::map work here? It doesn't seem like we need the ID
allocation feature, right?

[Zhiqiang Zhang (Slow), 2016/06/30 12:46:54]

Actually it was suggested by jochen. IDMap allows the user to manage ids
themselves. IDMap says it is optimized for small data sets, which should be
effecient in our case.

[dcheng, 2016/07/01 05:57:59]

I just don't see much of a point to using IDMap here: we manage the IDs
ourselves and we don't need the 'safe to iterate while removing' behavior. My
general preference is to use something generic if I don't need the specialized
behavior, since it's more standard. For example, if this was using std::map, the
teardown in the dtor would just be a standard for-each loop.

[Zhiqiang Zhang (Slow), 2016/07/01 11:01:06]

OK, I agree with you. changed to std::map. But one thing to mention is that
erase using for-each loop will crash since the std::map::iterator will be
invalidated when the current iterator is being erased.

+      static_cast<WebContentsImpl*>(contents_), pp_instance), pp_instance);
+  MediaSession::Get(contents_)->AddPlayer(
+      players_map_.Lookup(pp_instance), 0, MediaSession::Type::Content);

[dcheng, 2016/06/30 07:02:39]

Perhaps make 0 a constant so it's clear this is the player_id? I guess AddPlayer
/ RemovePlayer are keyed by both the observer and the player_id, so it's safe to
always use 0?

[Zhiqiang Zhang (Slow), 2016/06/30 12:46:54]

Done.

+}
+
+void PepperPlaybackObserver::PepperStopsPlayback(int32_t pp_instance) {
+  if (!players_map_.Lookup(pp_instance))
+    return;
+
+  MediaSession::Get(contents_)->RemovePlayer(
+      players_map_.Lookup(pp_instance), 0);
+
+  players_map_.Remove(pp_instance);
+}
+
+}  // namespace content