GitLab

Add generic getString and setString methods to PrefServiceBridge, making
use of the prefs.h enums.

Migrate Contextual Search related pref methods to use the generic
methods, and move the wrapper functions to ContextualSearchManager.

Bug: 1016957
Change-Id: I0da10f579f4021885929f99e16f6a949c1c5af9a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1879954
Commit-Queue: Natalie Chouinard <chouinard@chromium.org>
Reviewed-by: Theresa  <twellington@chromium.org>
Cr-Commit-Position: refs/heads/master@{#709525}