Allow ConnectionService to ask Telecomm for ringback

Cherry picked from branch lmp-preview-dev because checking the changes into master required an API update, whereas the relevant APIs are @hide-ed in the source branch.

Implements the necessary wiring to respond to a ConnectionService that
asks Telecomm to play ringbacks on its behalf.

Bug: 15190301
Change-Id: Ic6a6c031aa92df1f3587daf74f24d090cd21245b
(cherry picked from commit 50a57136b3aa876c8311b58e1e11720a337fe1cc)
diff --git a/src/com/android/telecomm/CallsManager.java b/src/com/android/telecomm/CallsManager.java
index e1d3044..e8b49e5 100644
--- a/src/com/android/telecomm/CallsManager.java
+++ b/src/com/android/telecomm/CallsManager.java
@@ -60,6 +60,7 @@
         void onIncomingCallRejected(Call call);
         void onForegroundCallChanged(Call oldForegroundCall, Call newForegroundCall);
         void onAudioStateChanged(CallAudioState oldAudioState, CallAudioState newAudioState);
+        void onRequestingRingback(Call call, boolean ringback);
     }
 
     private static final CallsManager INSTANCE = new CallsManager();
@@ -158,6 +159,13 @@
         call.removeListener(this);
     }
 
+    @Override
+    public void onRequestingRingback(Call call, boolean ringback) {
+        for (CallsManagerListener listener : mListeners) {
+            listener.onRequestingRingback(call, ringback);
+        }
+    }
+
     ImmutableCollection<Call> getCalls() {
         return ImmutableList.copyOf(mCalls);
     }