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

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=193020

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

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@193040 0039d316-1c4b-4281-b951-d872f2087c98

2 files changed, 10 insertions, 8 deletions

diff --git a/sync/engine/syncer_unittest.cc b/sync/engine/syncer_unittest.cc
index 5ee9e47..2dcc4b7 100644
--- a/sync/engine/syncer_unittest.cc
+++ b/sync/engine/syncer_unittest.cc
@@ -1641,15 +1641,15 @@ TEST_F(SyncerTest, TestCommitListOrderingAndNewParentAndChild) {
 
 TEST_F(SyncerTest, UpdateWithZeroLengthName) {
   // One illegal update
-  mock_server_->AddUpdateDirectory(1, 0, "", 1, 10,
-                                   foreign_cache_guid(), "-1");
+  mock_server_->AddUpdateDirectory(
+      1, 0, std::string(), 1, 10, foreign_cache_guid(), "-1");
   // And one legal one that we're going to delete.
   mock_server_->AddUpdateDirectory(2, 0, "FOO", 1, 10,
                                    foreign_cache_guid(), "-2");
   SyncShareNudge();
   // Delete the legal one. The new update has a null name.
-  mock_server_->AddUpdateDirectory(2, 0, "", 2, 20,
-                                   foreign_cache_guid(), "-2");
+  mock_server_->AddUpdateDirectory(
+      2, 0, std::string(), 2, 20, foreign_cache_guid(), "-2");
   mock_server_->SetLastUpdateDeleted();
   SyncShareNudge();
 }
@@ -4044,9 +4044,11 @@ TEST_F(SyncerTest, UniqueServerTagUpdates) {
   }
 
   // Now download some tagged items as updates.
-  mock_server_->AddUpdateDirectory(1, 0, "update1", 1, 10, "", "");
+  mock_server_->AddUpdateDirectory(
+      1, 0, "update1", 1, 10, std::string(), std::string());
   mock_server_->SetLastUpdateServerTag("alpha");
-  mock_server_->AddUpdateDirectory(2, 0, "update2", 2, 20, "", "");
+  mock_server_->AddUpdateDirectory(
+      2, 0, "update2", 2, 20, std::string(), std::string());
   mock_server_->SetLastUpdateServerTag("bob");
   SyncShareNudge();
 
@@ -4252,7 +4254,7 @@ TEST_F(SyncerTest, GetKeyEmpty) {
     EXPECT_TRUE(directory()->GetNigoriHandler()->NeedKeystoreKey(&rtrans));
   }
 
-  mock_server_->SetKeystoreKey("");
+  mock_server_->SetKeystoreKey(std::string());
   SyncShareConfigure();
 
   EXPECT_NE(session_->status_controller().last_get_key_result(), SYNCER_OK);
diff --git a/sync/engine/syncer_util.cc b/sync/engine/syncer_util.cc
index c571b10..d1bde98 100644
--- a/sync/engine/syncer_util.cc
+++ b/sync/engine/syncer_util.cc
@@ -633,7 +633,7 @@ VerifyResult VerifyUndelete(syncable::WriteTransaction* trans,
     DCHECK(target->Get(UNIQUE_CLIENT_TAG).empty())
         << "Doing move-aside undeletion on client-tagged item.";
     target->Put(ID, trans->directory()->NextId());
-    target->Put(UNIQUE_CLIENT_TAG, "");
+    target->Put(UNIQUE_CLIENT_TAG, std::string());
     target->Put(BASE_VERSION, CHANGES_VERSION);
     target->Put(SERVER_VERSION, 0);
     return VERIFY_SUCCESS;