GitLab

This CL ClearIndex function to Index and its subclasses. This function
clears all the data stored in the index.

Bug: 1132170
Change-Id: Idbec8ed4c721f09577b40c59b9cf24ebe5060252
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2428273Reviewed-by: Jia Meng <jiameng@chromium.org>
Commit-Queue: Thanh Nguyen <thanhdng@chromium.org>
Cr-Commit-Position: refs/heads/master@{#811136}