Retire ScopedObserver in /ios/chrome/browser/ui/settings.

ScopedObserver is being deprecated in favor of two new classes:
- base::ScopedObservation for observers that only ever observe
  a single source.
- base::ScopedMultiSourceObservation for observers that do or may
  observe more than a single source.

This CL was uploaded by git cl split.

R=jlebel@chromium.org

Bug: 1145565
Change-Id: I296cb59680ab26fdf4e45b0c2d245671742432cf
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2902628
Commit-Queue: Sigurður Ásgeirsson <siggi@chromium.org>
Commit-Queue: Jérôme <jlebel@chromium.org>
Auto-Submit: Sigurður Ásgeirsson <siggi@chromium.org>
Reviewed-by: Jérôme <jlebel@chromium.org>
Cr-Commit-Position: refs/heads/master@{#884133}
diff --git a/ios/chrome/browser/ui/settings/utils/content_setting_backed_boolean.mm b/ios/chrome/browser/ui/settings/utils/content_setting_backed_boolean.mm
index a0965f6..99da18f6 100644
--- a/ios/chrome/browser/ui/settings/utils/content_setting_backed_boolean.mm
+++ b/ios/chrome/browser/ui/settings/utils/content_setting_backed_boolean.mm
@@ -4,7 +4,7 @@
 
 #import "ios/chrome/browser/ui/settings/utils/content_setting_backed_boolean.h"
 
-#include "base/scoped_observer.h"
+#include "base/scoped_observation.h"
 #include "components/content_settings/core/browser/content_settings_details.h"
 #include "components/content_settings/core/browser/content_settings_observer.h"
 #include "components/content_settings/core/browser/host_content_settings_map.h"
@@ -32,8 +32,9 @@
 
 namespace {
 
-typedef ScopedObserver<HostContentSettingsMap, content_settings::Observer>
-    ContentSettingsObserver;
+typedef base::ScopedObservation<HostContentSettingsMap,
+                                content_settings::Observer>
+    ContentSettingsObseration;
 
 class ContentSettingsObserverBridge : public content_settings::Observer {
  public:
@@ -84,7 +85,7 @@
   ContentSettingsType _settingID;
   scoped_refptr<HostContentSettingsMap> _settingsMap;
   std::unique_ptr<ContentSettingsObserverBridge> _adaptor;
-  std::unique_ptr<ContentSettingsObserver> _content_settings_observer;
+  std::unique_ptr<ContentSettingsObseration> _content_settings_observer;
 }
 
 @synthesize settingID = _settingID;
@@ -103,8 +104,8 @@
     // Listen for changes to the content setting.
     _adaptor.reset(new ContentSettingsObserverBridge(self));
     _content_settings_observer.reset(
-        new ContentSettingsObserver(_adaptor.get()));
-    _content_settings_observer->Add(settingsMap);
+        new ContentSettingsObseration(_adaptor.get()));
+    _content_settings_observer->Observe(settingsMap);
   }
   return self;
 }