Rewrite std::string("") to std::string(), Linux edition.

This patch was generated by running the empty_string clang tool
across the Chromium Linux compilation database. Implicitly or
explicitly constructing std::string() with a "" argument is
inefficient as the caller needs to emit extra instructions to
pass an argument, and the constructor needlessly copies a byte
into internal storage. Rewriting these instances to simply call
the default constructor appears to save ~14-18 kilobytes on an
optimized release build.

BUG=none

Review URL: https://codereview.chromium.org/13145003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@193020 0039d316-1c4b-4281-b951-d872f2087c98

6 files changed, 29 insertions, 21 deletions

diff --git a/sync/notifier/p2p_invalidator.cc b/sync/notifier/p2p_invalidator.cc
index dd9a34d..7825757 100644
--- a/sync/notifier/p2p_invalidator.cc
+++ b/sync/notifier/p2p_invalidator.cc
@@ -40,7 +40,7 @@ std::string P2PNotificationTargetToString(P2PNotificationTarget target) {
       return kNotifyAll;
     default:
       NOTREACHED();
-      return "";
+      return std::string();
   }
 }
 
@@ -171,8 +171,9 @@ void P2PInvalidator::UpdateRegisteredIds(InvalidationHandler* handler,
                       ObjectIdLessThan());
   registrar_.UpdateRegisteredIds(handler, ids);
   const P2PNotificationData notification_data(
-      invalidator_client_id_, NOTIFY_SELF,
-      ObjectIdSetToInvalidationMap(new_ids, ""));
+      invalidator_client_id_,
+      NOTIFY_SELF,
+      ObjectIdSetToInvalidationMap(new_ids, std::string()));
   SendNotificationData(notification_data);
 }
 
@@ -224,8 +225,10 @@ void P2PInvalidator::OnNotificationsEnabled() {
   registrar_.UpdateInvalidatorState(INVALIDATIONS_ENABLED);
   if (just_turned_on) {
     const P2PNotificationData notification_data(
-        invalidator_client_id_, NOTIFY_SELF,
-        ObjectIdSetToInvalidationMap(registrar_.GetAllRegisteredIds(), ""));
+        invalidator_client_id_,
+        NOTIFY_SELF,
+        ObjectIdSetToInvalidationMap(registrar_.GetAllRegisteredIds(),
+                                     std::string()));
     SendNotificationData(notification_data);
   }
 }
@@ -256,10 +259,11 @@ void P2PInvalidator::OnIncomingNotification(
   if (!notification_data.ResetFromString(notification.data)) {
     LOG(WARNING) << "Could not parse notification data from "
                  << notification.data;
-    notification_data =
-        P2PNotificationData(
-            invalidator_client_id_, NOTIFY_ALL,
-            ObjectIdSetToInvalidationMap(registrar_.GetAllRegisteredIds(), ""));
+    notification_data = P2PNotificationData(
+        invalidator_client_id_,
+        NOTIFY_ALL,
+        ObjectIdSetToInvalidationMap(registrar_.GetAllRegisteredIds(),
+                                     std::string()));
   }
   if (!notification_data.IsTargeted(invalidator_client_id_)) {
     DVLOG(1) << "Not a target of the notification -- "
diff --git a/sync/notifier/p2p_invalidator_unittest.cc b/sync/notifier/p2p_invalidator_unittest.cc
index 1b7aad4..6acc3d1 100644
--- a/sync/notifier/p2p_invalidator_unittest.cc
+++ b/sync/notifier/p2p_invalidator_unittest.cc
@@ -69,7 +69,7 @@ class P2PInvalidatorTestDelegate {
   void TriggerOnIncomingInvalidation(
       const ObjectIdInvalidationMap& invalidation_map) {
     const P2PNotificationData notification_data(
-        "", NOTIFY_ALL, invalidation_map);
+        std::string(), NOTIFY_ALL, invalidation_map);
     notifier::Notification notification;
     notification.channel = kSyncP2PNotificationChannel;
     notification.data = notification_data.ToString();
@@ -160,7 +160,7 @@ TEST_F(P2PInvalidatorTest, P2PNotificationDataIsTargeted) {
 // default-constructed P2PNotificationData.
 TEST_F(P2PInvalidatorTest, P2PNotificationDataDefault) {
   const P2PNotificationData notification_data;
-  EXPECT_TRUE(notification_data.IsTargeted(""));
+  EXPECT_TRUE(notification_data.IsTargeted(std::string()));
   EXPECT_FALSE(notification_data.IsTargeted("other1"));
   EXPECT_FALSE(notification_data.IsTargeted("other2"));
   EXPECT_TRUE(notification_data.GetIdInvalidationMap().empty());
@@ -179,7 +179,8 @@ TEST_F(P2PInvalidatorTest, P2PNotificationDataDefault) {
 TEST_F(P2PInvalidatorTest, P2PNotificationDataNonDefault) {
   const ObjectIdInvalidationMap& invalidation_map =
       ObjectIdSetToInvalidationMap(
-          ModelTypeSetToObjectIdSet(ModelTypeSet(BOOKMARKS, THEMES)), "");
+          ModelTypeSetToObjectIdSet(ModelTypeSet(BOOKMARKS, THEMES)),
+          std::string());
   const P2PNotificationData notification_data(
       "sender", NOTIFY_ALL, invalidation_map);
   EXPECT_TRUE(notification_data.IsTargeted("sender"));
@@ -247,7 +248,8 @@ TEST_F(P2PInvalidatorTest, NotificationsBasic) {
   {
     const ObjectIdInvalidationMap& invalidation_map =
         ObjectIdSetToInvalidationMap(
-            ModelTypeSetToObjectIdSet(ModelTypeSet(THEMES, APPS)), "");
+            ModelTypeSetToObjectIdSet(ModelTypeSet(THEMES, APPS)),
+            std::string());
     invalidator->SendInvalidation(invalidation_map);
   }
 
@@ -264,8 +266,8 @@ TEST_F(P2PInvalidatorTest, SendNotificationData) {
   const ModelTypeSet expected_types(THEMES);
 
   const ObjectIdInvalidationMap& invalidation_map =
-      ObjectIdSetToInvalidationMap(
-          ModelTypeSetToObjectIdSet(changed_types), "");
+      ObjectIdSetToInvalidationMap(ModelTypeSetToObjectIdSet(changed_types),
+                                   std::string());
 
   P2PInvalidator* const invalidator = delegate_.GetInvalidator();
   notifier::FakePushClient* const push_client = delegate_.GetPushClient();
diff --git a/sync/notifier/push_client_channel_unittest.cc b/sync/notifier/push_client_channel_unittest.cc
index ffe90e7..d017e1b 100644
--- a/sync/notifier/push_client_channel_unittest.cc
+++ b/sync/notifier/push_client_channel_unittest.cc
@@ -73,7 +73,7 @@ TEST_F(PushClientChannelTest, EncodeDecode) {
 TEST_F(PushClientChannelTest, EncodeDecodeNoContext) {
   const notifier::Notification& notification =
       PushClientChannel::EncodeMessageForTest(
-          kMessage, "", kSchedulingHash);
+          kMessage, std::string(), kSchedulingHash);
   std::string message;
   std::string service_context = kServiceContext;
   int64 scheduling_hash = kSchedulingHash + 1;
diff --git a/sync/notifier/sync_invalidation_listener_unittest.cc b/sync/notifier/sync_invalidation_listener_unittest.cc
index 8177327..dba4728 100644
--- a/sync/notifier/sync_invalidation_listener_unittest.cc
+++ b/sync/notifier/sync_invalidation_listener_unittest.cc
@@ -148,7 +148,7 @@ class FakeDelegate : public SyncInvalidationListener::Delegate {
 
   std::string GetPayload(const ObjectId& id) const {
     ObjectIdInvalidationMap::const_iterator it = invalidations_.find(id);
-    return (it == invalidations_.end()) ? "" : it->second.payload;
+    return (it == invalidations_.end()) ? std::string() : it->second.payload;
   }
 
   InvalidatorState GetInvalidatorState() const {
diff --git a/sync/notifier/sync_system_resources.cc b/sync/notifier/sync_system_resources.cc
index 5328657..3fc31fc 100644
--- a/sync/notifier/sync_system_resources.cc
+++ b/sync/notifier/sync_system_resources.cc
@@ -181,14 +181,15 @@ void SyncStorage::SetSystemResources(
 
 void SyncStorage::RunAndDeleteWriteKeyCallback(
     invalidation::WriteKeyCallback* callback) {
-  callback->Run(invalidation::Status(invalidation::Status::SUCCESS, ""));
+  callback->Run(
+      invalidation::Status(invalidation::Status::SUCCESS, std::string()));
   delete callback;
 }
 
 void SyncStorage::RunAndDeleteReadKeyCallback(
     invalidation::ReadKeyCallback* callback, const std::string& value) {
   callback->Run(std::make_pair(
-      invalidation::Status(invalidation::Status::SUCCESS, ""),
+      invalidation::Status(invalidation::Status::SUCCESS, std::string()),
       value));
   delete callback;
 }
diff --git a/sync/notifier/sync_system_resources_unittest.cc b/sync/notifier/sync_system_resources_unittest.cc
index 77423b3..cb406da 100644
--- a/sync/notifier/sync_system_resources_unittest.cc
+++ b/sync/notifier/sync_system_resources_unittest.cc
@@ -168,9 +168,10 @@ TEST_F(SyncSystemResourcesTest, WriteState) {
   EXPECT_CALL(mock_storage_callback, Run(_))
       .WillOnce(SaveArg<0>(&results));
   sync_system_resources_.storage()->WriteKey(
-      "", "state", mock_storage_callback.CreateCallback());
+      std::string(), "state", mock_storage_callback.CreateCallback());
   message_loop_.RunUntilIdle();
-  EXPECT_EQ(invalidation::Status(invalidation::Status::SUCCESS, ""), results);
+  EXPECT_EQ(invalidation::Status(invalidation::Status::SUCCESS, std::string()),
+            results);
 }
 
 }  // namespace