Shield settings are not saved after restart browser

[yrliou]

STR:

1. Open any page and set its shield setting
2. Restart the browser

expected result: the setting is the same as the setting before restarting the browser
actual result: its shield setting is the same as our default shield setting, not the saved one

[srirambv]

Possible duplicate of #52?

[yrliou]

@srirambv #52 is because fingerprinting protection & block phishing aren't actually implemented but just a UI stub, this issue is opened for all shield settings and focused on restoring saved settings after browser restart.
Fixing #11 (which PRs are currently under review) will solve the fingerprinting protection part of #52.

[srirambv]

Sounds good 👍

[btlechowski]

Verification passed on

Brave	0.55.5 Chromium: 70.0.3538.16 (Official Build) dev (64-bit)
Revision	16ed95b41bb05e565b11fb66ac33c660b721f778-refs/branch-heads/3538@{#306}
OS	Windows 7

Verification Passed on

Brave	0.55.5 Chromium: 70.0.3538.16 (Official Build) dev (64-bit)
Revision	16ed95b41bb05e565b11fb66ac33c660b721f778-refs/branch-heads/3538@{#306}
OS	Linux

Verified passed with

Brave	0.55.10 Chromium: 70.0.3538.22 (Official Build) beta(64-bit)
Revision	ac9418ba9c3bd7f6baaffa0b055dfe147e0f8364-refs/branch-heads/3538@{#468}
OS	Mac OS X