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

5 files changed, 7 insertions, 7 deletions

diff --git a/base/metrics/field_trial.cc b/base/metrics/field_trial.cc
index 4ab5ff9..1f4f9ae 100644
--- a/base/metrics/field_trial.cc
+++ b/base/metrics/field_trial.cc
@@ -318,7 +318,7 @@ std::string FieldTrialList::FindFullName(const std::string& name) {
   FieldTrial* field_trial = Find(name);
   if (field_trial)
     return field_trial->group_name();
-  return "";
+  return std::string();
 }
 
 // static
diff --git a/base/metrics/field_trial_unittest.cc b/base/metrics/field_trial_unittest.cc
index 81c4f37..bb2c39f 100644
--- a/base/metrics/field_trial_unittest.cc
+++ b/base/metrics/field_trial_unittest.cc
@@ -86,7 +86,7 @@ TEST_F(FieldTrialTest, Registration) {
   EXPECT_EQ(name1, trial1->trial_name());
   EXPECT_EQ("", trial1->group_name_internal());
 
-  trial1->AppendGroup("", 7);
+  trial1->AppendGroup(std::string(), 7);
 
   EXPECT_EQ(trial1, FieldTrialList::Find(name1));
   EXPECT_FALSE(FieldTrialList::Find(name2));
@@ -221,7 +221,7 @@ TEST_F(FieldTrialTest, OneWinner) {
   std::string winner_name;
 
   for (int i = 1; i <= group_count; ++i) {
-    int might_win = trial->AppendGroup("", 1);
+    int might_win = trial->AppendGroup(std::string(), 1);
 
     // Because we keep appending groups, we want to see if the last group that
     // was added has been assigned or not.
diff --git a/base/metrics/statistics_recorder.cc b/base/metrics/statistics_recorder.cc
index f6174f3..13aeeb7 100644
--- a/base/metrics/statistics_recorder.cc
+++ b/base/metrics/statistics_recorder.cc
@@ -308,7 +308,7 @@ StatisticsRecorder::~StatisticsRecorder() {
   DCHECK(histograms_ && ranges_ && lock_);
   if (dump_on_exit_) {
     string output;
-    WriteGraph("", &output);
+    WriteGraph(std::string(), &output);
     DLOG(INFO) << output;
   }
 
diff --git a/base/metrics/stats_counters.cc b/base/metrics/stats_counters.cc
index f763220..12416d9 100644
--- a/base/metrics/stats_counters.cc
+++ b/base/metrics/stats_counters.cc
@@ -45,7 +45,7 @@ int* StatsCounter::GetPtr() {
   if (counter_id_ == -1) {
     counter_id_ = table->FindCounter(name_);
     if (table->GetSlot() == 0) {
-      if (!table->RegisterThread("")) {
+      if (!table->RegisterThread(std::string())) {
         // There is no room for this thread.  This thread
         // cannot use counters.
         counter_id_ = 0;
diff --git a/base/metrics/stats_table.cc b/base/metrics/stats_table.cc
index dede1e4..9585863 100644
--- a/base/metrics/stats_table.cc
+++ b/base/metrics/stats_table.cc
@@ -431,8 +431,8 @@ int* StatsTable::FindLocation(const char* name) {
   // Get the slot for this thread.  Try to register
   // it if none exists.
   int slot = table->GetSlot();
-  if (!slot && !(slot = table->RegisterThread("")))
-      return NULL;
+  if (!slot && !(slot = table->RegisterThread(std::string())))
+    return NULL;
 
   // Find the counter id for the counter.
   std::string str_name(name);