AudioSystem: new audioflinger restart detection

Add a specific method to AudioSystem for AudioService to poll
for AudioFlinger service restart instead of relying on current
callback mechanism which is flaky.

Bug: 9693068.
Change-Id: Ie88bc9d25033503bc5cd2fa9d8c754d0f8045b8f
diff --git a/media/libmedia/AudioSystem.cpp b/media/libmedia/AudioSystem.cpp
index a571fe4..8033c2c 100644
--- a/media/libmedia/AudioSystem.cpp
+++ b/media/libmedia/AudioSystem.cpp
@@ -76,6 +76,14 @@
     return gAudioFlinger;
 }
 
+/* static */ status_t AudioSystem::checkAudioFlinger()
+{
+    if (defaultServiceManager()->checkService(String16("media.audio_flinger")) != 0) {
+        return NO_ERROR;
+    }
+    return DEAD_OBJECT;
+}
+
 status_t AudioSystem::muteMicrophone(bool state) {
     const sp<IAudioFlinger>& af = AudioSystem::get_audio_flinger();
     if (af == 0) return PERMISSION_DENIED;