Use version 3 for DisableExtensions not 2

We already shipped a chrome version with version 2 exposed, so the
Chrome Cleanup Tool will try to use this method when it doesn't exist
unless we bump the minimum version.

Change-Id: I6c0bf1209da85ea54f4e7d2d365d64ac8a98ba66
Bug: 889568
Reviewed-on: https://chromium-review.googlesource.com/1258296
Commit-Queue: Preston Carpenter <timidger@google.com>
Reviewed-by: Will Harris <wfh@chromium.org>
Reviewed-by: Joe Mason <joenotcharles@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#596254}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 0a78043deb1840d45ef6a4ee262ad0fc3b223709