This is both an optimisation and a cleanup.

This converts code like
   aStr.indexOf("XX") == 0
to
  aStr.startsWith("XX")
and converts code like
  aStr.lastIndexOf("XXX") == aStr.getLength() - 3
to
  aStr.endsWith("XXX")

Note that in general
  aStr.lastIndexOf("X") == aStr.getLength() - 1
converts to
  aStr.isEmpty() || aStr.endsWith("X")
so I used the surrounding context to determine if aStr could be empty
when modifying the code.

Change-Id: I22cb8ca7c2a4d0288b001f72adb27fd63af87669