Add comment detailing MAX_RANGE

Followup on ag/20930150; add a comment to explain why we need to
limit the amount of ranges.

Bug: 220115129
Test: no code change, only a comment
Change-Id: I7ce1ebdc1c1dcd5474639ec9506b0e5b9df02498

core/java/android/view/InputDevice.java

@@ -446,6 +446,7 @@ public final class InputDevice implements Parcelable {
      */
     public static final int KEYBOARD_TYPE_ALPHABETIC = 2;
 
+    // Cap motion ranges to prevent attacks (b/25637534)
     private static final int MAX_RANGES = 1000;
 
     private static final int VIBRATOR_ID_ALL = -1;