[Extensions] Reduce string copy in renderer/ UserScript.

extensions/renderer/programmatic_script_injector.cc

Index: extensions/renderer/programmatic_script_injector.cc
diff --git a/extensions/renderer/programmatic_script_injector.cc b/extensions/renderer/programmatic_script_injector.cc
index e52885eee742fe261107ff1040b6628d9e532a83..9cd4f9f3a37bb7ee05e8284ac84d278fdd191b64 100644
--- a/extensions/renderer/programmatic_script_injector.cc
+++ b/extensions/renderer/programmatic_script_injector.cc
@@ -104,12 +104,13 @@ std::vector<blink::WebScriptSource> ProgrammaticScriptInjector::GetJsSources(
           blink::WebString::fromUTF8(params_->code), params_->file_url));
 }
 
-std::vector<std::string> ProgrammaticScriptInjector::GetCssSources(
+std::vector<blink::WebString> ProgrammaticScriptInjector::GetCssSources(
     UserScript::RunLocation run_location) const {
   DCHECK_EQ(GetRunLocation(), run_location);
   DCHECK(!params_->is_javascript);
 
-  return std::vector<std::string>(1, params_->code);
+  return std::vector<blink::WebString>(
+      1, blink::WebString::fromUTF8(params_->code));
 }
 
 void ProgrammaticScriptInjector::GetRunInfo(