Add haptic effect for the seekbar in Settings 2/n.

- for Audio balance, perform haptic feedback as the seekbar's progress value is the center/min/max value.
- screenshot, https://screenshot.googleplex.com/3xJUJkvJuXTUCqe

Bug: 174109628
Test: make -j42 RunSettingsRoboTests ROBOTEST_FILTER=BalanceSeekBarTest
Change-Id: I8b4ab37a2e635fb3b1ca2a9277a06b1e83f81bbb

src/com/android/settings/accessibility/BalanceSeekBar.java

@@ -16,6 +16,7 @@
 
 package com.android.settings.accessibility;
 
+import static android.view.HapticFeedbackConstants.CLOCK_TICK;
 import static com.android.settings.Utils.isNightMode;
 
 import android.content.Context;
@@ -44,6 +45,7 @@ public class BalanceSeekBar extends SeekBar {
     private final Context mContext;
     private final Object mListenerLock = new Object();
     private OnSeekBarChangeListener mOnSeekBarChangeListener;
+    private int mLastProgress = -1;
     private final OnSeekBarChangeListener mProxySeekBarListener = new OnSeekBarChangeListener() {
         @Override
         public void onStopTrackingTouch(SeekBar seekBar) {
@@ -73,6 +75,12 @@ public class BalanceSeekBar extends SeekBar {
                     progress = mCenter;
                     seekBar.setProgress(progress); // direct update (fromUser becomes false)
                 }
+                if (progress != mLastProgress) {
+                    if (progress == mCenter || progress == getMin() || progress == getMax()) {
+                        seekBar.performHapticFeedback(CLOCK_TICK);
+                    }
+                    mLastProgress = progress;
+                }
                 final float balance = (progress - mCenter) * 0.01f;
                 Settings.System.putFloatForUser(mContext.getContentResolver(),
                         Settings.System.MASTER_BALANCE, balance, UserHandle.USER_CURRENT);
@@ -152,10 +160,5 @@ public class BalanceSeekBar extends SeekBar {
         canvas.restore();
         super.onDraw(canvas);
     }
-
-    @VisibleForTesting
-    OnSeekBarChangeListener getProxySeekBarListener() {
-        return mProxySeekBarListener;
-    }
 }