Add haptic effect for the seekbar in Settings 4/n.

- in Font size/Display size, perform haptic feedback as the seekbar's progress value is updated.
- screenshot, https://screenshot.googleplex.com/6tcD7a9hvCcWaui
- screenshot, https://screenshot.googleplex.com/89y4Q3RXskyajnL

Bug: 174109628
Test: make -j42 RunSettingsRoboTests ROBOTEST_FILTER=LabeledSeekBarTest
Change-Id: I7aff859e4fdaed6fe95a5d77564059ef1a7f6ff0

src/com/android/settings/widget/LabeledSeekBar.java

@@ -16,6 +16,8 @@
 
 package com.android.settings.widget;
 
+import static android.view.HapticFeedbackConstants.CLOCK_TICK;
+
 import android.content.Context;
 import android.graphics.Rect;
 import android.os.Bundle;
@@ -48,6 +50,8 @@ public class LabeledSeekBar extends SeekBar {
     /** Labels for discrete progress values. */
     private String[] mLabels;
 
+    private int mLastProgress = -1;
+
     public LabeledSeekBar(Context context, AttributeSet attrs) {
         this(context, attrs, com.android.internal.R.attr.seekBarStyle);
     }
@@ -118,6 +122,10 @@ public class LabeledSeekBar extends SeekBar {
                 mOnSeekBarChangeListener.onProgressChanged(seekBar, progress, fromUser);
                 sendClickEventForAccessibility(progress);
             }
+            if (progress != mLastProgress) {
+                seekBar.performHapticFeedback(CLOCK_TICK);
+                mLastProgress = progress;
+            }
         }
     };