Expose a meta-data value to allow dialer ringing

This CL exposes a new meta-data, IN_CALL_SERVICE_RINGING. If this is set
to true then ringing is played by the dialer instead of Telecom.

This CL also adds a new silenceRinger() API to InCallService. This is
needed to implement ringer silence on volume key down.

BUG: 22857261
Change-Id: I498538282eddbb727104f5b879f25adbef4e6cf6
diff --git a/telecomm/java/android/telecom/Phone.java b/telecomm/java/android/telecom/Phone.java
index 47154da..56eb7ec 100644
--- a/telecomm/java/android/telecom/Phone.java
+++ b/telecomm/java/android/telecom/Phone.java
@@ -97,6 +97,13 @@
          * @param canAddCall Indicates whether an additional call can be added.
          */
         public void onCanAddCallChanged(Phone phone, boolean canAddCall) { }
+
+        /**
+         * Called to silence the ringer if a ringing call exists.
+         *
+         * @param phone The {@code Phone} calling this method.
+         */
+        public void onSilenceRinger(Phone phone) { }
     }
 
     // A Map allows us to track each Call by its Telecom-specified call ID
@@ -179,6 +186,10 @@
         }
     }
 
+    final void internalSilenceRinger() {
+        fireSilenceRinger();
+    }
+
     /**
      * Called to destroy the phone and cleanup any lingering calls.
      */
@@ -330,6 +341,12 @@
         }
     }
 
+    private void fireSilenceRinger() {
+        for (Listener listener : mListeners) {
+            listener.onSilenceRinger(this);
+        }
+    }
+
     private void checkCallTree(ParcelableCall parcelableCall) {
         if (parcelableCall.getParentCallId() != null &&
                 !mCallByTelecomCallId.containsKey(parcelableCall.getParentCallId())) {