Various optimizations to reduce the number of temporary allocations.

chrome/browser/extensions/api/font_settings/font_settings_api.cc

Index: chrome/browser/extensions/api/font_settings/font_settings_api.cc
diff --git a/chrome/browser/extensions/api/font_settings/font_settings_api.cc b/chrome/browser/extensions/api/font_settings/font_settings_api.cc
index cf01a958e33df9ba0d82949357627cf7e80edca3..0a6381daa5b0cd960ccc5856ae42a0111781158f 100644
--- a/chrome/browser/extensions/api/font_settings/font_settings_api.cc
+++ b/chrome/browser/extensions/api/font_settings/font_settings_api.cc
@@ -61,8 +61,8 @@ std::string GetFontNamePrefPath(fonts::GenericFamily generic_family_enum,
     script = prefs::kWebKitCommonScript;
   std::string generic_family = fonts::ToString(generic_family_enum);
   return base::StringPrintf(kWebKitFontPrefFormat,
-                            generic_family.c_str(),
-                            script.c_str());
+                            generic_family,
+                            script);
 }
 
 // Returns the localized name of a font so that it can be matched within the
@@ -84,10 +84,11 @@ void RegisterFontFamilyMapObserver(
     PrefChangeRegistrar* registrar,
     const char* map_name,
     const PrefChangeRegistrar::NamedChangeCallback& callback) {
+  std::string pref_name;

[Nico, 2014/12/03 21:16:46]

Now that I look at it again: This is unused.

   for (size_t i = 0; i < prefs::kWebKitScriptsForFontFamilyMapsLength; ++i) {
     const char* script = prefs::kWebKitScriptsForFontFamilyMaps[i];
     std::string pref_name = base::StringPrintf("%s.%s", map_name, script);

[Peter Kasting, 2014/12/03 21:21:03]

You're shadowing the outer variable with this inner one.  I think you want to
remove the type here.  (This is Nico's complaint, but with the opposite
resolution.  However, see next comment.)

-    registrar->Add(pref_name.c_str(), callback);
+    registrar->Add(pref_name, callback);

[Peter Kasting, 2014/12/03 21:21:03]

What's the perf of just doing:

  registrar->Add(base::StringPrintf("%s.%s", map_name, script), callback);

?  If StringPrintf() has to construct an output string anyway, I can't imagine
that this is more allocations than the way you've written the code currently,
and it's shorter and avoids the somewhat confusing-looking declaration of
pref_name above the loop (I would normally see this code and move the
declaration back in to comply with the style guide's rule to "declare variables
in the most local scope").

[Georges Khalil, 2014/12/03 21:58:32]

Agreed, no impact on performance. Done. Hope that works for you too Nico! :)

   }
 }
 
@@ -109,21 +110,21 @@ FontSettingsEventRouter::FontSettingsEventRouter(
 
   PrefChangeRegistrar::NamedChangeCallback callback =
       base::Bind(&FontSettingsEventRouter::OnFontFamilyMapPrefChanged,
-                 base::Unretained(this));
-  RegisterFontFamilyMapObserver(&registrar_,
-                                prefs::kWebKitStandardFontFamilyMap, callback);
-  RegisterFontFamilyMapObserver(&registrar_,
-                                prefs::kWebKitSerifFontFamilyMap, callback);
-  RegisterFontFamilyMapObserver(&registrar_,
-                                prefs::kWebKitSansSerifFontFamilyMap, callback);
-  RegisterFontFamilyMapObserver(&registrar_,
-                                prefs::kWebKitFixedFontFamilyMap, callback);
-  RegisterFontFamilyMapObserver(&registrar_,
-                                prefs::kWebKitCursiveFontFamilyMap, callback);
-  RegisterFontFamilyMapObserver(&registrar_,
-                                prefs::kWebKitFantasyFontFamilyMap, callback);
-  RegisterFontFamilyMapObserver(&registrar_,
-                                prefs::kWebKitPictographFontFamilyMap,
+                 base::Unretained(this));
+  RegisterFontFamilyMapObserver(&registrar_,
+                                prefs::kWebKitStandardFontFamilyMap, callback);
+  RegisterFontFamilyMapObserver(&registrar_,
+                                prefs::kWebKitSerifFontFamilyMap, callback);
+  RegisterFontFamilyMapObserver(&registrar_,
+                                prefs::kWebKitSansSerifFontFamilyMap, callback);
+  RegisterFontFamilyMapObserver(&registrar_,
+                                prefs::kWebKitFixedFontFamilyMap, callback);
+  RegisterFontFamilyMapObserver(&registrar_,
+                                prefs::kWebKitCursiveFontFamilyMap, callback);
+  RegisterFontFamilyMapObserver(&registrar_,
+                                prefs::kWebKitFantasyFontFamilyMap, callback);
+  RegisterFontFamilyMapObserver(&registrar_,
+                                prefs::kWebKitPictographFontFamilyMap,
                                 callback);
 }
 
@@ -156,7 +157,7 @@ void FontSettingsEventRouter::OnFontNamePrefChanged(
     const std::string& generic_family,
     const std::string& script) {
   const PrefService::Preference* pref = registrar_.prefs()->FindPreference(
-      pref_name.c_str());
+      pref_name);
   CHECK(pref);
 
   std::string font_name;
@@ -187,7 +188,7 @@ void FontSettingsEventRouter::OnFontPrefChanged(
     const std::string& key,
     const std::string& pref_name) {
   const PrefService::Preference* pref = registrar_.prefs()->FindPreference(
-      pref_name.c_str());
+      pref_name);
   CHECK(pref);
 
   base::ListValue args;
@@ -235,10 +236,10 @@ bool FontSettingsClearFontFunction::RunSync() {
 
   // Ensure |pref_path| really is for a registered per-script font pref.
   EXTENSION_FUNCTION_VALIDATE(
-      GetProfile()->GetPrefs()->FindPreference(pref_path.c_str()));
+      GetProfile()->GetPrefs()->FindPreference(pref_path));
 
   PreferenceAPI::Get(GetProfile())->RemoveExtensionControlledPref(
-      extension_id(), pref_path.c_str(), kExtensionPrefsScopeRegular);
+      extension_id(), pref_path, kExtensionPrefsScopeRegular);
   return true;
 }
 
@@ -252,7 +253,7 @@ bool FontSettingsGetFontFunction::RunSync() {
 
   PrefService* prefs = GetProfile()->GetPrefs();
   const PrefService::Preference* pref =
-      prefs->FindPreference(pref_path.c_str());
+      prefs->FindPreference(pref_path);
 
   std::string font_name;
   EXTENSION_FUNCTION_VALIDATE(
@@ -288,11 +289,11 @@ bool FontSettingsSetFontFunction::RunSync() {
 
   // Ensure |pref_path| really is for a registered font pref.
   EXTENSION_FUNCTION_VALIDATE(
-      GetProfile()->GetPrefs()->FindPreference(pref_path.c_str()));
+      GetProfile()->GetPrefs()->FindPreference(pref_path));
 
   PreferenceAPI::Get(GetProfile())->SetExtensionControlledPref(
       extension_id(),
-      pref_path.c_str(),
+      pref_path,
       kExtensionPrefsScopeRegular,
       new base::StringValue(params->details.font_id));
   return true;