Add webkit.webprefs.javascript_can_access_clipboard

This pref is already defined, but is not able to be
set in <user-data-dir>/Default/Preferences.
It is used often in conjunction with
webkit.webprefs.dom_paste_enabled, and it is helpful
to be able to set both during development with either
cmdline switch or in prefs file.

This field was added in CL
https://chromium.googlesource.com/chromium/src/+/a4898ce4a26204138b0e47e1fb6ac59eeb00e1c8%5E%21/

Bug: 813477
Change-Id: I61769ca8fbd989b5833717d53c8cd2495d05028c
Reviewed-on: https://chromium-review.googlesource.com/1006561
Reviewed-by: Dominic Battré <battre@chromium.org>
Commit-Queue: Joel Hockey <joelhockey@chromium.org>
Cr-Commit-Position: refs/heads/master@{#549845}
4 files changed