Merge "Add indexOf method" am: 2318c7f334 am: 334a56ba7d

Original change: https://android-review.googlesource.com/c/platform/frameworks/libs/net/+/1560368

MUST ONLY BE SUBMITTED BY AUTOMERGER

Change-Id: Iaae2cc70b299b924991263d942097096f6b5f0b5