Introduce CaptureStateNotifier

This is a helper class for notifying a client of capture
state changes.

Bug: 146157104
Test: Compiles (further testing as part of the topic).
Change-Id: Ie27bc404805d319a6969290a6369d59fb68c1f38
Merged-In: Ie27bc404805d319a6969290a6369d59fb68c1f38
diff --git a/services/audiopolicy/service/Android.bp b/services/audiopolicy/service/Android.bp
index 1a08eb1..35a4599 100644
--- a/services/audiopolicy/service/Android.bp
+++ b/services/audiopolicy/service/Android.bp
@@ -6,6 +6,7 @@
         "AudioPolicyEffects.cpp",
         "AudioPolicyInterfaceImpl.cpp",
         "AudioPolicyService.cpp",
+        "CaptureStateNotifier.cpp",
     ],
 
     include_dirs: [