Add UI for the cursorToolOnLoad pref in the UI of the Chrome extension.
Add logic to migrate the enableHandToolOnLoad pref to cursorToolOnLoad.
For past values in the mutable extension storage area:
1. If enableHandToolOnLoad=true, save cursorToolOnLoad=1.
2. Remove enableHandToolOnLoad.
For the managed extension storage, which is immutable since it is based
on administrative policies, use the following logic:
1. If enableHandToolOnLoad=true and cursorToolOnLoad=0 (default).
set cursorToolOnLoad=0 and assume enableHandToolOnLoad=false.
2. As usual, managed preferences can (and will) be overridden by the user.
The first migration logic is in extensions/chromium/options/migration.js
and can be removed after a few months / less than many years.
The second migration logic is in web/chromecom.js, and should be kept
around for a long while (many years).
The need for this migration logic arises from the change by:
https://github.com/mozilla/pdf.js/pull/7635
Commit df10513e10 unfortunately broke the options dialog of the Chromium extension because the logic required to work with the preference was not added. This patch adds the required logic to show the preference in the options dialog and to persist it to the preferences storage.
Verified using Chromium 50 on Arch Linux.
