Migrate might_have_observer to empty in components/services/app_service

Bug: 1155308
Change-Id: I3dddd787488aeea1d82fb50f48dd469f49acb5a0
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2637088Reviewed-by: Dominick Ng <dominickn@chromium.org>
Commit-Queue: Mitsuru Oshima <oshima@chromium.org>
Cr-Commit-Position: refs/heads/master@{#845214}

components/services/app_service/public/cpp/app_registry_cache.cc

@@ -40,7 +40,7 @@ AppRegistryCache::~AppRegistryCache() {
   for (auto& obs : observers_) {
     obs.OnAppRegistryCacheWillBeDestroyed(this);
   }
-  DCHECK(!observers_.might_have_observers());
+  DCHECK(observers_.empty());
 }
 
 void AppRegistryCache::AddObserver(Observer* observer) {

components/services/app_service/public/cpp/instance_registry.cc

@@ -44,7 +44,7 @@ InstanceRegistry::~InstanceRegistry() {
   for (auto& obs : observers_) {
     obs.OnInstanceRegistryWillBeDestroyed(this);
   }
-  DCHECK(!observers_.might_have_observers());
+  DCHECK(observers_.empty());
 }
 
 void InstanceRegistry::AddObserver(Observer* observer) {