Replace OVERRIDE with their C++11 counterparts in extensions

This is fix for newly added OVERRIDE construts in extensions folder.
This step is a giant search and replace for OVERRIDE and FINAL to
replace them with their lowercase versions.

BUG=417463

Review URL: https://codereview.chromium.org/658453002

Cr-Commit-Position: refs/heads/master@{#299448}
1 file changed