Migrate might_have_observer to empty in components/policy

Bug: 1155308
Change-Id: I07590fea32455cdecb4e9d9ed62af1e202871040
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2637089Reviewed-by: Sergey Poromov <poromov@chromium.org>
Commit-Queue: Mitsuru Oshima <oshima@chromium.org>
Cr-Commit-Position: refs/heads/master@{#845244}

components/policy/core/browser/configuration_policy_pref_store.cc

@@ -70,7 +70,7 @@ void ConfigurationPolicyPrefStore::RemoveObserver(
 }
 
 bool ConfigurationPolicyPrefStore::HasObservers() const {
-  return observers_.might_have_observers();
+  return !observers_.empty();
 }
 
 bool ConfigurationPolicyPrefStore::IsInitializationComplete() const {

components/policy/core/common/policy_service_impl.cc

@@ -235,7 +235,7 @@ void PolicyServiceImpl::RemoveObserver(PolicyDomain domain,
   if (it == observers_.end())
     return;
   it->second->RemoveObserver(observer);
-  if (!it->second->might_have_observers()) {
+  if (it->second->empty()) {
     observers_.erase(it);
   }
 }