CEC: Comment for clarification of <Text View On>

Added a comment to clarify how the service is designed to handle
CEC commands <Text View On>/<Image View On>.

Bug: 24690166
Change-Id: Iaa1813b3ded76e8525141555d2aaff6dfb67888d
(cherry picked from commit 6667797016a28551202b40067fe90512185a7a61)
diff --git a/services/core/java/com/android/server/hdmi/HdmiCecLocalDeviceTv.java b/services/core/java/com/android/server/hdmi/HdmiCecLocalDeviceTv.java
index cb56b35..cd8484f 100644
--- a/services/core/java/com/android/server/hdmi/HdmiCecLocalDeviceTv.java
+++ b/services/core/java/com/android/server/hdmi/HdmiCecLocalDeviceTv.java
@@ -732,6 +732,14 @@
     @ServiceThreadOnly
     protected boolean handleTextViewOn(HdmiCecMessage message) {
         assertRunOnServiceThread();
+
+        // Note that <Text View On> (and <Image View On>) command won't be handled here in
+        // most cases. A dedicated microcontroller should be in charge while Android system
+        // is in sleep mode, and the command need not be passed up to this service.
+        // The only situation where the command reaches this handler is that sleep mode is
+        // implemented in such a way that Android system is not really put to standby mode
+        // but only the display is set to blank. Then the command leads to the effect of
+        // turning on the display by the invocation of PowerManager.wakeUp().
         if (mService.isPowerStandbyOrTransient() && mAutoWakeup) {
             mService.wakeUp();
         }