Stub out new A/B test opt-in setting. Add draft strings for it.

_locales/en/messages.json

@@ -947,6 +947,9 @@
 	"settings_allow_offers": {
 		"message": "Participating in Ghostery Rewards"
 	},
+  	"settings_allow_abtests": {
+	  	"message": "Participating in A/B Tests"
+	},
 	"settings_signin_create_header": {
 		"message": "Sign In / Create Account"
 	},
@@ -1037,6 +1040,9 @@
 	"settings_offers_tooltip": {
 		"message": "Ghostery Rewards is a private-by-design feature that delivers you discounts and special offers from our partner companies as you browse."
 	},
+  	"settings_abtests_tooltip": {
+	  	"message": "Participating in A/B tests helps Ghostery understand which version of a new layout or feature users like you prefer. The testing mechanism uses a random number generated on install to determine which version of a beta feature you see."
+	},
 	"settings_opt_in": {
 		"message": "Opt In / Out"
 	},

app/panel/components/Settings/OptIn.jsx

@@ -85,6 +85,12 @@ const OptIn = ({ settingsData, toggleCheckbox }) => {
 						tooltipSVG(t('settings_offers_tooltip'), 'up'),
 						'offers-section'
 					)}
+					{!IS_CLIQZ && option(
+						checkbox('allow-abtests', true),
+						labelFor('allow-abtests', t('settings_allow_abtests')),
+						tooltipSVG(t('settings_abtests_tooltip'), 'up'),
+						'abtests-section'
+					)}
 				</div>
 			</div>
 		</div>