Retire ScopedObserver in /components/performance_manager.

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=chrisha@chromium.org

Bug: 1145565
Change-Id: Ib6367ca00891ceb30f937f01977cc98895fc942d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2532720
Auto-Submit: Sigurður Ásgeirsson <siggi@chromium.org>
Reviewed-by: Chris Hamilton <chrisha@chromium.org>
Commit-Queue: Chris Hamilton <chrisha@chromium.org>
Cr-Commit-Position: refs/heads/master@{#826561}

components/performance_manager/persistence/site_data/site_data_cache_impl.h

@@ -15,7 +15,7 @@
 #include "base/files/file_path.h"
 #include "base/gtest_prod_util.h"
 #include "base/macros.h"
-#include "base/scoped_observer.h"
+#include "base/scoped_observation.h"
 #include "base/sequence_checker.h"
 #include "components/performance_manager/persistence/site_data/site_data_cache.h"
 #include "components/performance_manager/persistence/site_data/site_data_cache_inspector.h"

components/performance_manager/service_worker_context_adapter.cc

@@ -6,7 +6,7 @@
 
 #include "base/check_op.h"
 #include "base/notreached.h"
-#include "base/scoped_observer.h"
+#include "base/scoped_observation.h"
 #include "content/public/browser/render_process_host.h"
 #include "content/public/browser/render_process_host_observer.h"