[Android] Take over pref changes from settings opt-in

|prefs::kContextualSearchEnabled| is added to the list of synced
prefs that are observed during settings opt-in.

Bug: 933647
Change-Id: I3db775f98127286971cd5a1e3b2d5ddeee583959
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1538530Reviewed-by: Boris Sazonov <bsazonov@chromium.org>
Reviewed-by: Theresa <twellington@chromium.org>
Commit-Queue: Thomas Tangl <tangltom@chromium.org>
Cr-Commit-Position: refs/heads/master@{#644786}

chrome/android/java/res/xml/sync_and_services_preferences.xml

@@ -3,6 +3,10 @@
      Use of this source code is governed by a BSD-style license that can be
      found in the LICENSE file. -->
 
+<!-- Note: If a synced pref is added/removed from this file, the method
+     |GetSyncedServicePrefNames| in
+     chrome/browser/unified_consent/unified_consent_service_factory.cc has to be
+     updated accordingly. -->
 <PreferenceScreen xmlns:android="http://schemas.android.com/apk/res/android">
     <org.chromium.chrome.browser.preferences.SignInPreference
         android:key="sign_in"

chrome/browser/unified_consent/unified_consent_service_factory.cc

@@ -4,6 +4,7 @@
 
 #include "chrome/browser/unified_consent/unified_consent_service_factory.h"
 
+#include "build/build_config.h"
 #include "chrome/browser/prefs/pref_service_syncable_util.h"
 #include "chrome/browser/profiles/profile.h"
 #include "chrome/browser/signin/identity_manager_factory.h"
@@ -26,12 +27,20 @@ namespace {
 // Returns the synced pref names of the services on the "Sync and Google
 // services" settings page.
 // Note: The synced prefs returned by this method have to match the prefs
-// shown in personalization_options.html.
+// shown in
+// chrome/browser/resources/settings/privacy_page/personalization_options.html
+// on Desktop and chrome/android/java/res/xml/sync_and_services_preferences.xml
+// on Android.
+
 std::vector<std::string> GetSyncedServicePrefNames() {
-  return {prefs::kSearchSuggestEnabled, prefs::kAlternateErrorPagesEnabled,
-          prefs::kSafeBrowsingEnabled,
-          prefs::kSafeBrowsingScoutReportingEnabled,
-          spellcheck::prefs::kSpellCheckUseSpellingService};
+  return {
+    prefs::kSearchSuggestEnabled, prefs::kAlternateErrorPagesEnabled,
+        prefs::kSafeBrowsingEnabled, prefs::kSafeBrowsingScoutReportingEnabled,
+        spellcheck::prefs::kSpellCheckUseSpellingService,
+#if defined(OS_ANDROID)
+        prefs::kContextualSearchEnabled
+#endif
+  };
 }
 
 }  // namespace