ash: Explicitly enumerate repeatable accelerators.

Instead of designating specific accelerators as
non-repeatable (which is prone to getting outdated), keep
track of the few accelerators that should be repeatable.

Also make many probably-inadvertently-repeatable
accelerators instead be non-repeatable.

BUG=626014
TEST=manual

Review-Url: https://codereview.chromium.org/2130603002
Cr-Commit-Position: refs/heads/master@{#404161}
6 files changed