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

3 files changed, 10 insertions, 9 deletions

diff --git a/jingle/notifier/base/gaia_token_pre_xmpp_auth.cc b/jingle/notifier/base/gaia_token_pre_xmpp_auth.cc
index 24aa6a9..f7ddf8d 100644
--- a/jingle/notifier/base/gaia_token_pre_xmpp_auth.cc
+++ b/jingle/notifier/base/gaia_token_pre_xmpp_auth.cc
@@ -101,9 +101,10 @@ std::string GaiaTokenPreXmppAuth::GetAuthMechanism() const {
 
 std::string GaiaTokenPreXmppAuth::ChooseBestSaslMechanism(
     const std::vector<std::string> & mechanisms, bool encrypted) {
-  return (std::find(mechanisms.begin(),
-                    mechanisms.end(), auth_mechanism_) !=
-          mechanisms.end()) ? auth_mechanism_ : "";
+  return (std::find(mechanisms.begin(), mechanisms.end(), auth_mechanism_) !=
+              mechanisms.end())
+             ? auth_mechanism_
+             : std::string();
 }
 
 buzz::SaslMechanism* GaiaTokenPreXmppAuth::CreateSaslMechanism(
diff --git a/jingle/notifier/communicator/single_login_attempt.cc b/jingle/notifier/communicator/single_login_attempt.cc
index dda0cfe..49fcdee 100644
--- a/jingle/notifier/communicator/single_login_attempt.cc
+++ b/jingle/notifier/communicator/single_login_attempt.cc
@@ -85,9 +85,9 @@ net::HostPortPair ParseRedirectText(const std::string& redirect_text) {
 void SingleLoginAttempt::OnError(buzz::XmppEngine::Error error, int subcode,
                                  const buzz::XmlElement* stream_error) {
   DVLOG(1) << "Error: " << error << ", subcode: " << subcode
-           << (stream_error ?
-               (", stream error: " + XmlElementToString(*stream_error)) :
-               "");
+           << (stream_error
+                   ? (", stream error: " + XmlElementToString(*stream_error))
+                   : std::string());
 
   DCHECK_EQ(error == buzz::XmppEngine::ERROR_STREAM, stream_error != NULL);
 
diff --git a/jingle/notifier/communicator/single_login_attempt_unittest.cc b/jingle/notifier/communicator/single_login_attempt_unittest.cc
index 582b808..4d009c2 100644
--- a/jingle/notifier/communicator/single_login_attempt_unittest.cc
+++ b/jingle/notifier/communicator/single_login_attempt_unittest.cc
@@ -219,7 +219,7 @@ TEST_F(SingleLoginAttemptTest, RedirectInvalidPort) {
 // Fire an empty redirect and make sure the delegate does not get a
 // redirect.
 TEST_F(SingleLoginAttemptTest, RedirectEmpty) {
-  scoped_ptr<buzz::XmlElement> redirect_error(MakeRedirectError(""));
+  scoped_ptr<buzz::XmlElement> redirect_error(MakeRedirectError(std::string()));
   FireRedirect(redirect_error.get());
   EXPECT_EQ(IDLE, fake_delegate_.state());
 }
@@ -227,7 +227,7 @@ TEST_F(SingleLoginAttemptTest, RedirectEmpty) {
 // Fire a redirect with a missing text element and make sure the
 // delegate does not get a redirect.
 TEST_F(SingleLoginAttemptTest, RedirectMissingText) {
-  scoped_ptr<buzz::XmlElement> redirect_error(MakeRedirectError(""));
+  scoped_ptr<buzz::XmlElement> redirect_error(MakeRedirectError(std::string()));
   redirect_error->RemoveChildAfter(redirect_error->FirstChild());
   FireRedirect(redirect_error.get());
   EXPECT_EQ(IDLE, fake_delegate_.state());
@@ -236,7 +236,7 @@ TEST_F(SingleLoginAttemptTest, RedirectMissingText) {
 // Fire a redirect with a missing see-other-host element and make sure
 // the delegate does not get a redirect.
 TEST_F(SingleLoginAttemptTest, RedirectMissingSeeOtherHost) {
-  scoped_ptr<buzz::XmlElement> redirect_error(MakeRedirectError(""));
+  scoped_ptr<buzz::XmlElement> redirect_error(MakeRedirectError(std::string()));
   redirect_error->RemoveChildAfter(NULL);
   FireRedirect(redirect_error.get());
   EXPECT_EQ(IDLE, fake_delegate_.state());