Make DefaultPrefStore::ReplaceDefaultValue() more efficient.

Fix some other nits in prefs code too.

Change-Id: If08a48575024d8e338cc5ef009ba8535627584dd
Reviewed-on: https://chromium-review.googlesource.com/721805Reviewed-by: Bernhard Bauer <bauerb@chromium.org>
Commit-Queue: Lei Zhang <thestig@chromium.org>
Cr-Commit-Position: refs/heads/master@{#509487}

components/prefs/default_pref_store.cc

@@ -35,16 +35,14 @@ bool DefaultPrefStore::HasObservers() const {
 
 void DefaultPrefStore::SetDefaultValue(const std::string& key,
                                        std::unique_ptr<Value> value) {
-  DCHECK(!GetValue(key, NULL));
+  DCHECK(!GetValue(key, nullptr));
   prefs_.SetValue(key, std::move(value));
 }
 
 void DefaultPrefStore::ReplaceDefaultValue(const std::string& key,
                                            std::unique_ptr<Value> value) {
-  const Value* old_value = NULL;
-  GetValue(key, &old_value);
-  bool notify = !old_value->Equals(value.get());
-  prefs_.SetValue(key, std::move(value));
+  DCHECK(GetValue(key, nullptr));
+  bool notify = prefs_.SetValue(key, std::move(value));
   if (notify) {
     for (Observer& observer : observers_)
       observer.OnPrefValueChanged(key);

components/prefs/pref_registry.cc

@@ -14,8 +14,7 @@
 #include "components/prefs/pref_store.h"
 
 PrefRegistry::PrefRegistry()
-    : defaults_(new DefaultPrefStore()) {
-}
+    : defaults_(base::MakeRefCounted<DefaultPrefStore>()) {}
 
 PrefRegistry::~PrefRegistry() {
 }
@@ -23,9 +22,7 @@ PrefRegistry::~PrefRegistry() {
 uint32_t PrefRegistry::GetRegistrationFlags(
     const std::string& pref_name) const {
   const auto& it = registration_flags_.find(pref_name);
-  if (it == registration_flags_.end())
-    return NO_REGISTRATION_FLAGS;
-  return it->second;
+  return it != registration_flags_.end() ? it->second : NO_REGISTRATION_FLAGS;
 }
 
 scoped_refptr<PrefStore> PrefRegistry::defaults() {