[unified-consent] Add learn-more URL to settings page

A learn-more question mark is added to the syncSetup page.

Bug: 863138
Cq-Include-Trybots: luci.chromium.try:closure_compilation
Change-Id: I3da65e76a7054c6c5256dc96f746c83968dc2e28
Reviewed-on: https://chromium-review.googlesource.com/1138247Reviewed-by: Scott Chen <scottchen@chromium.org>
Commit-Queue: Thomas Tangl <tangltom@chromium.org>
Cr-Commit-Position: refs/heads/master@{#575348}

chrome/browser/resources/settings/people_page/people_page.html

@@ -354,6 +354,7 @@
         <settings-subpage
             associated-control="[[$$('#sync-status')]]"
             page-title="$i18n{syncPageTitle}"
+            learn-more-url="$i18n{privacyLearnMoreURL}"
             no-search$="[[!isAdvancedSyncSettingsVisible_(syncStatus,
                 unifiedConsentEnabled_)]]">
           <settings-sync-page

chrome/browser/ui/webui/settings/md_settings_localized_strings_provider.cc

@@ -1974,6 +1974,7 @@ void AddPrivacyStrings(content::WebUIDataSource* html_source,
                             arraysize(conditional_localized_strings));
   }
 
+  html_source->AddString("privacyLearnMoreURL", chrome::kPrivacyLearnMoreURL);
   html_source->AddString(
       "improveBrowsingExperience",
       l10n_util::GetStringFUTF16(