[Magnifier] Don't include focus following result when screen magnifier disabled

Don't include focus following result "Magnifier follows keyboard focus" in Chrome OS Settings search results when screen magnifier is disabled.

Before: https://screenshot.googleplex.com/7k4npcGDnBznceP
After: https://screenshot.googleplex.com/5Gmmstz22u7Dcfi

AX-Relnotes: N/A.
Fixed: 1165652
Change-Id: Ibb7dd1c7b7e301c0322d09615765484205958d3e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2623429
Commit-Queue: Josiah Krutz <josiahk@google.com>
Auto-Submit: Josiah Krutz <josiahk@google.com>
Reviewed-by: David Tseng <dtseng@chromium.org>
Reviewed-by: Jimmy Gong <jimmyxgong@chromium.org>
Cr-Commit-Position: refs/heads/master@{#843212}

chrome/browser/ui/webui/settings/chromeos/accessibility_section.cc

@@ -368,6 +368,10 @@ AccessibilitySection::AccessibilitySection(
       ash::prefs::kAccessibilitySwitchAccessAutoScanEnabled,
       base::BindRepeating(&AccessibilitySection::UpdateSearchTags,
                           base::Unretained(this)));
+  pref_change_registrar_.Add(
+      ash::prefs::kAccessibilityScreenMagnifierEnabled,
+      base::BindRepeating(&AccessibilitySection::UpdateSearchTags,
+                          base::Unretained(this)));
 
   UpdateSearchTags();
 
@@ -826,7 +830,9 @@ void AccessibilitySection::UpdateSearchTags() {
     updater.RemoveSearchTags(GetA11yLiveCaptionSearchConcepts());
   }
 
-  if (IsMagnifierPanningImprovementsEnabled()) {
+  if (IsMagnifierPanningImprovementsEnabled() &&
+      pref_service_->GetBoolean(
+          ash::prefs::kAccessibilityScreenMagnifierEnabled)) {
     updater.AddSearchTags(
         GetA11yFullscreenMagnifierFocusFollowingSearchConcepts());
   } else {