CEC: Implement handleReportArcInitiate method

Bug: 159901363
Test: None

Change-Id: Ibdff6d2c83d945f487312a14b577ace0636d7b02

services/core/java/com/android/server/hdmi/HdmiCecLocalDeviceAudioSystem.java

@@ -358,8 +358,12 @@ public class HdmiCecLocalDeviceAudioSystem extends HdmiCecLocalDeviceSource {
     @Constants.HandleMessageResult
     protected int handleReportArcInitiate(HdmiCecMessage message) {
         assertRunOnServiceThread();
-        // TODO(amyjojo): implement report arc initiate handler
-        HdmiLogger.debug(TAG + "Stub handleReportArcInitiate");
+        /*
+         * Ideally, we should have got this response before the {@link ArcInitiationActionFromAvr}
+         * has timed out. Even if the response is late, {@link ArcInitiationActionFromAvr
+         * #handleInitiateArcTimeout()} would not have disabled ARC. So nothing needs to be done
+         * here.
+         */
         return Constants.HANDLED;
     }