Refresh app-bound encryption metrics and re-enable them.

The data format for encryption and decryption has changed, as
well as a few issues being resolved.

In order to gather even more data, this CL changes the pref name
(again) and wipes existing data (again) in order to get a full
Encrypt and Decrypt cycle from all clients.

Existing metrics are also renamed to ensure it is possible to
distinguish clients running the newest code from older ones.

Finally, the metrics are enabled by the feature in chrome/browser.

BUG=41493095
OBSOLETE_HISTOGRAMS=OSCrypt.AppBoundEncryption.PathValidation histograms were all replaced by versions with '2' appended to them.

Change-Id: I9e4a621b4ef18b0aa9da4bd99d51b54db182213d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5394193


Reviewed-by: Robert Kaplow <rkaplow@chromium.org>
Commit-Queue: Will Harris <wfh@chromium.org>
Reviewed-by: Scott Violet <sky@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1278448}