Web MIDI: add dynamic MidiManager instantiation support for Linux

media/midi/midi_manager.cc

Index: media/midi/midi_manager.cc
diff --git a/media/midi/midi_manager.cc b/media/midi/midi_manager.cc
index 95a48401c09781a26f3fceff88153bff45c03b0e..89d640ef320a42c0a67ebbab81d96bb9523d77c2 100644
--- a/media/midi/midi_manager.cc
+++ b/media/midi/midi_manager.cc
@@ -72,15 +72,24 @@ void MidiManager::Shutdown() {
   UMA_HISTOGRAM_ENUMERATION("Media.Midi.ResultOnShutdown",
                             static_cast<int>(result_),
                             static_cast<int>(Result::MAX) + 1);
-  base::AutoLock auto_lock(lock_);
-  if (session_thread_runner_) {
-    session_thread_runner_->PostTask(
-        FROM_HERE, base::Bind(&MidiManager::ShutdownOnSessionThread,
-                              base::Unretained(this)));
-    session_thread_runner_ = nullptr;
-  } else {
-    finalized_ = true;
+  bool shutdown_synchronously = false;
+  {
+    base::AutoLock auto_lock(lock_);
+    if (session_thread_runner_) {
+      if (session_thread_runner_->BelongsToCurrentThread()) {
+        shutdown_synchronously = true;
+      } else {
+        session_thread_runner_->PostTask(
+            FROM_HERE, base::Bind(&MidiManager::ShutdownOnSessionThread,
+                                  base::Unretained(this)));
+      }
+      session_thread_runner_ = nullptr;
+    } else {
+      finalized_ = true;
+    }
   }
+  if (shutdown_synchronously)
+    ShutdownOnSessionThread();
 }
 
 void MidiManager::StartSession(MidiManagerClient* client) {