Add a clarifying comment

Bug: 130332550
Test: no test
Change-Id: If6dea9b5deab35f8c2da1019c17be80bbf1c5fd8

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

@@ -129,6 +129,13 @@ public abstract class VibrationPreferenceFragment extends RadioButtonPickerFragm
             Settings.System.putInt(getContext().getContentResolver(),
                     getVibrationIntensitySetting(), candidate.getIntensity());
         } else {
+            // We can't play preview effect here for all cases because that causes a data race
+            // (VibratorService may access intensity settings before these settings are updated).
+            // But we can't just play it in intensity settings update observer, because the
+            // intensity settings are not changed if we turn the vibration off, then on.
+            //
+            // In this case we sould play the preview here.
+            // To be refactored in b/132952771
             playVibrationPreview();
         }
     }