Retire ScopedObserver in /components/unified_consent.

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=tangltom@chromium.org

Bug: 1145565
Change-Id: Ic7a1ab744690cf6d3ab830baf4b2f2a9474bb8a3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2532661
Auto-Submit: Sigurður Ásgeirsson <siggi@chromium.org>
Commit-Queue: Thomas Tangl <tangltom@chromium.org>
Reviewed-by: Thomas Tangl <tangltom@chromium.org>
Cr-Commit-Position: refs/heads/master@{#826767}

components/unified_consent/unified_consent_service.cc

@@ -6,7 +6,7 @@
 
 #include "base/check_op.h"
 #include "base/metrics/histogram_macros.h"
-#include "base/scoped_observer.h"
+#include "base/scoped_observation.h"
 #include "base/threading/sequenced_task_runner_handle.h"
 #include "build/build_config.h"
 #include "components/pref_registry/pref_registry_syncable.h"