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, 35 insertions, 28 deletions

diff --git a/extensions/common/extension_resource_unittest.cc b/extensions/common/extension_resource_unittest.cc
index 132e718..3791b14 100644
--- a/extensions/common/extension_resource_unittest.cc
+++ b/extensions/common/extension_resource_unittest.cc
@@ -131,7 +131,8 @@ TEST(ExtensionResourceTest, CreateWithAllResourcesOnDisk) {
   ASSERT_TRUE(file_util::CreateDirectory(l10n_path));
 
   std::vector<std::string> locales;
-  l10n_util::GetParentLocales(l10n_util::GetApplicationLocale(""), &locales);
+  l10n_util::GetParentLocales(l10n_util::GetApplicationLocale(std::string()),
+                              &locales);
   ASSERT_FALSE(locales.empty());
   for (size_t i = 0; i < locales.size(); i++) {
     base::FilePath make_path;
diff --git a/extensions/common/matcher/substring_set_matcher_unittest.cc b/extensions/common/matcher/substring_set_matcher_unittest.cc
index 4152ff9..fde65bf 100644
--- a/extensions/common/matcher/substring_set_matcher_unittest.cc
+++ b/extensions/common/matcher/substring_set_matcher_unittest.cc
@@ -117,7 +117,7 @@ TEST(SubstringSetMatcherTest, TestMatcher) {
   // String    abcde
   // Pattern 1
   // Pattern 2 abcdef
-  TestTwoPatterns("abcde", "", "abcdef", true, false);
+  TestTwoPatterns("abcde", std::string(), "abcdef", true, false);
 }
 
 TEST(SubstringSetMatcherTest, RegisterAndRemove) {
diff --git a/extensions/common/matcher/url_matcher.cc b/extensions/common/matcher/url_matcher.cc
index d7779a2..b599293 100644
--- a/extensions/common/matcher/url_matcher.cc
+++ b/extensions/common/matcher/url_matcher.cc
@@ -256,8 +256,8 @@ URLMatcherConditionFactory::~URLMatcherConditionFactory() {
 std::string URLMatcherConditionFactory::CanonicalizeURLForComponentSearches(
     const GURL& url) const {
   return kBeginningOfURL + CanonicalizeHostname(url.host()) + kEndOfDomain +
-      url.path() + kEndOfPath + (url.has_query() ? "?" + url.query() : "") +
-      kEndOfURL;
+         url.path() + kEndOfPath +
+         (url.has_query() ? "?" + url.query() : std::string()) + kEndOfURL;
 }
 
 URLMatcherCondition URLMatcherConditionFactory::CreateHostPrefixCondition(
diff --git a/extensions/common/matcher/url_matcher_factory.cc b/extensions/common/matcher/url_matcher_factory.cc
index cdd08ba..3ca4aa2 100644
--- a/extensions/common/matcher/url_matcher_factory.cc
+++ b/extensions/common/matcher/url_matcher_factory.cc
@@ -151,7 +151,8 @@ URLMatcherFactory::CreateFromURLFilterDictionary(
   // matched.
   if (url_matcher_conditions.empty()) {
     url_matcher_conditions.insert(
-        url_matcher_condition_factory->CreateHostPrefixCondition(""));
+        url_matcher_condition_factory->CreateHostPrefixCondition(
+            std::string()));
   }
 
   scoped_refptr<URLMatcherConditionSet> url_matcher_condition_set(
diff --git a/extensions/common/matcher/url_matcher_unittest.cc b/extensions/common/matcher/url_matcher_unittest.cc
index 09fc562..b17c13c 100644
--- a/extensions/common/matcher/url_matcher_unittest.cc
+++ b/extensions/common/matcher/url_matcher_unittest.cc
@@ -247,7 +247,7 @@ TEST(URLMatcherConditionFactoryTest, TestComponentSearches) {
   std::string url = factory.CanonicalizeURLForComponentSearches(gurl);
 
   // Test host component.
-  EXPECT_TRUE(Matches(factory.CreateHostPrefixCondition(""), url));
+  EXPECT_TRUE(Matches(factory.CreateHostPrefixCondition(std::string()), url));
   EXPECT_TRUE(Matches(factory.CreateHostPrefixCondition("www.goog"), url));
   EXPECT_TRUE(
       Matches(factory.CreateHostPrefixCondition("www.google.com"), url));
@@ -258,7 +258,7 @@ TEST(URLMatcherConditionFactoryTest, TestComponentSearches) {
       Matches(factory.CreateHostPrefixCondition("www.google.com/"), url));
   EXPECT_FALSE(Matches(factory.CreateHostPrefixCondition("webhp"), url));
 
-  EXPECT_TRUE(Matches(factory.CreateHostSuffixCondition(""), url));
+  EXPECT_TRUE(Matches(factory.CreateHostSuffixCondition(std::string()), url));
   EXPECT_TRUE(Matches(factory.CreateHostSuffixCondition("com"), url));
   EXPECT_TRUE(Matches(factory.CreateHostSuffixCondition(".com"), url));
   EXPECT_TRUE(
@@ -270,7 +270,7 @@ TEST(URLMatcherConditionFactoryTest, TestComponentSearches) {
       Matches(factory.CreateHostSuffixCondition("www.google.com/"), url));
   EXPECT_FALSE(Matches(factory.CreateHostSuffixCondition("webhp"), url));
 
-  EXPECT_FALSE(Matches(factory.CreateHostEqualsCondition(""), url));
+  EXPECT_FALSE(Matches(factory.CreateHostEqualsCondition(std::string()), url));
   EXPECT_FALSE(Matches(factory.CreateHostEqualsCondition("www"), url));
   EXPECT_TRUE(
       Matches(factory.CreateHostEqualsCondition("www.google.com"), url));
@@ -279,14 +279,14 @@ TEST(URLMatcherConditionFactoryTest, TestComponentSearches) {
 
 
   // Test path component.
-  EXPECT_TRUE(Matches(factory.CreatePathPrefixCondition(""), url));
+  EXPECT_TRUE(Matches(factory.CreatePathPrefixCondition(std::string()), url));
   EXPECT_TRUE(Matches(factory.CreatePathPrefixCondition("/web"), url));
   EXPECT_TRUE(Matches(factory.CreatePathPrefixCondition("/webhp"), url));
   EXPECT_FALSE(Matches(factory.CreatePathPrefixCondition("webhp"), url));
   EXPECT_FALSE(Matches(factory.CreatePathPrefixCondition("/webhp?"), url));
   EXPECT_FALSE(Matches(factory.CreatePathPrefixCondition("?sourceid"), url));
 
-  EXPECT_TRUE(Matches(factory.CreatePathSuffixCondition(""), url));
+  EXPECT_TRUE(Matches(factory.CreatePathSuffixCondition(std::string()), url));
   EXPECT_TRUE(Matches(factory.CreatePathSuffixCondition("webhp"), url));
   EXPECT_TRUE(Matches(factory.CreatePathSuffixCondition("/webhp"), url));
   EXPECT_FALSE(Matches(factory.CreatePathSuffixCondition("/web"), url));
@@ -300,12 +300,12 @@ TEST(URLMatcherConditionFactoryTest, TestComponentSearches) {
 
 
   // Test query component.
-  EXPECT_TRUE(Matches(factory.CreateQueryPrefixCondition(""), url));
+  EXPECT_TRUE(Matches(factory.CreateQueryPrefixCondition(std::string()), url));
   EXPECT_TRUE(Matches(factory.CreateQueryPrefixCondition("sourceid"), url));
   // The '?' at the beginning is just ignored.
   EXPECT_TRUE(Matches(factory.CreateQueryPrefixCondition("?sourceid"), url));
 
-  EXPECT_TRUE(Matches(factory.CreateQuerySuffixCondition(""), url));
+  EXPECT_TRUE(Matches(factory.CreateQuerySuffixCondition(std::string()), url));
   EXPECT_TRUE(Matches(factory.CreateQuerySuffixCondition("ion=1"), url));
   EXPECT_FALSE(Matches(factory.CreateQuerySuffixCondition("www"), url));
   // "Suffix" condition + pattern starting with '?' = "equals" condition.
@@ -330,21 +330,26 @@ TEST(URLMatcherConditionFactoryTest, TestComponentSearches) {
   // Test adjacent components
   EXPECT_TRUE(Matches(factory.CreateHostSuffixPathPrefixCondition(
       "google.com", "/webhp"), url));
-  EXPECT_TRUE(Matches(factory.CreateHostSuffixPathPrefixCondition(
-      "", "/webhp"), url));
-  EXPECT_TRUE(Matches(factory.CreateHostSuffixPathPrefixCondition(
-      "google.com", ""), url));
-  EXPECT_FALSE(Matches(factory.CreateHostSuffixPathPrefixCondition(
-      "www", ""), url));
+  EXPECT_TRUE(Matches(
+      factory.CreateHostSuffixPathPrefixCondition(std::string(), "/webhp"),
+      url));
+  EXPECT_TRUE(Matches(
+      factory.CreateHostSuffixPathPrefixCondition("google.com", std::string()),
+      url));
+  EXPECT_FALSE(Matches(
+      factory.CreateHostSuffixPathPrefixCondition("www", std::string()), url));
 
   EXPECT_TRUE(Matches(factory.CreateHostEqualsPathPrefixCondition(
       "www.google.com", "/webhp"), url));
-  EXPECT_FALSE(Matches(factory.CreateHostEqualsPathPrefixCondition(
-      "", "/webhp"), url));
+  EXPECT_FALSE(Matches(
+      factory.CreateHostEqualsPathPrefixCondition(std::string(), "/webhp"),
+      url));
   EXPECT_TRUE(Matches(factory.CreateHostEqualsPathPrefixCondition(
-      "www.google.com", ""), url));
-  EXPECT_FALSE(Matches(factory.CreateHostEqualsPathPrefixCondition(
-      "google.com", ""), url));
+                          "www.google.com", std::string()),
+                      url));
+  EXPECT_FALSE(Matches(
+      factory.CreateHostEqualsPathPrefixCondition("google.com", std::string()),
+      url));
 }
 
 TEST(URLMatcherConditionFactoryTest, TestFullSearches) {
@@ -354,9 +359,9 @@ TEST(URLMatcherConditionFactoryTest, TestFullSearches) {
   URLMatcherConditionFactory factory;
   std::string url = factory.CanonicalizeURLForFullSearches(gurl);
 
-  EXPECT_TRUE(Matches(factory.CreateURLPrefixCondition(""), url));
-  EXPECT_TRUE(Matches(factory.CreateURLPrefixCondition(
-      "https://www.goog"), url));
+  EXPECT_TRUE(Matches(factory.CreateURLPrefixCondition(std::string()), url));
+  EXPECT_TRUE(
+      Matches(factory.CreateURLPrefixCondition("https://www.goog"), url));
   EXPECT_TRUE(Matches(factory.CreateURLPrefixCondition(
       "https://www.google.com"), url));
   EXPECT_TRUE(Matches(factory.CreateURLPrefixCondition(
@@ -365,11 +370,11 @@ TEST(URLMatcherConditionFactoryTest, TestFullSearches) {
       "http://www.google.com"), url));
   EXPECT_FALSE(Matches(factory.CreateURLPrefixCondition("webhp"), url));
 
-  EXPECT_TRUE(Matches(factory.CreateURLSuffixCondition(""), url));
+  EXPECT_TRUE(Matches(factory.CreateURLSuffixCondition(std::string()), url));
   EXPECT_TRUE(Matches(factory.CreateURLSuffixCondition("ion=1"), url));
   EXPECT_FALSE(Matches(factory.CreateURLSuffixCondition("www"), url));
 
-  EXPECT_TRUE(Matches(factory.CreateURLContainsCondition(""), url));
+  EXPECT_TRUE(Matches(factory.CreateURLContainsCondition(std::string()), url));
   EXPECT_TRUE(Matches(factory.CreateURLContainsCondition("www.goog"), url));
   EXPECT_TRUE(Matches(factory.CreateURLContainsCondition("webhp"), url));
   EXPECT_TRUE(Matches(factory.CreateURLContainsCondition("?"), url));