Allow the down volume key to silence notifs

Additionally preserve existing behavior by passing
the keypress on.

Fixes: 130025623
Test: manual
Change-Id: I00f83275000369c1ab03bae63eb0a4b6170c4b53
(cherry picked from commit deb2d0b743e14871b964b30ad791ac5ff0cde016)
diff --git a/core/java/android/app/INotificationManager.aidl b/core/java/android/app/INotificationManager.aidl
index e57738f..9f51db8 100644
--- a/core/java/android/app/INotificationManager.aidl
+++ b/core/java/android/app/INotificationManager.aidl
@@ -108,6 +108,8 @@
     ParceledListSlice getNotificationChannelsBypassingDnd(String pkg, int userId);
     boolean isPackagePaused(String pkg);
 
+    void silenceNotificationSound();
+
     // TODO: Remove this when callers have been migrated to the equivalent
     // INotificationListener method.
     @UnsupportedAppUsage
diff --git a/core/java/android/app/NotificationManager.java b/core/java/android/app/NotificationManager.java
index dd39376..b13a34f 100644
--- a/core/java/android/app/NotificationManager.java
+++ b/core/java/android/app/NotificationManager.java
@@ -1095,6 +1095,25 @@
     }
 
     /**
+     * Silences the current notification sound, if ones currently playing.
+     * <p>
+     * It is intended to handle use-cases such as silencing a ringing call
+     * when the user presses the volume button during ringing.
+     * <p>
+     * If this method is called prior to when the notification begins playing, the sound will not be
+     * silenced.  As such it is not intended as a means to avoid playing of a sound.
+     * @hide
+     */
+    public void silenceNotificationSound() {
+        INotificationManager service = getService();
+        try {
+            service.silenceNotificationSound();
+        } catch (RemoteException e) {
+            throw e.rethrowFromSystemServer();
+        }
+    }
+
+    /**
      * Returns whether notifications from this package are temporarily hidden. This
      * could be done because the package was marked as distracting to the user via
      * {@code PackageManager#setDistractingPackageRestrictions(String[], int)} or because the