[Service Workers] DCHECK from WebServiceWorkerResponse::visitHTTPHeaderFields.

content/renderer/service_worker/service_worker_type_util.cc

Index: content/renderer/service_worker/service_worker_type_util.cc
diff --git a/content/renderer/service_worker/service_worker_type_util.cc b/content/renderer/service_worker/service_worker_type_util.cc
index 720ea2d32a58d56496c197610ee5bca04a63620d..9e5878f2e5fdaa1a47100590a14b254b2e0c8503 100644
--- a/content/renderer/service_worker/service_worker_type_util.cc
+++ b/content/renderer/service_worker/service_worker_type_util.cc
@@ -25,10 +25,9 @@ class HeaderVisitor : public blink::WebHTTPHeaderVisitor {
 
   void visitHeader(const blink::WebString& name,
                    const blink::WebString& value) override {
-    const std::string header_name =
-        base::UTF16ToASCII(base::StringPiece16(name));
-    const std::string header_value =
-        base::UTF16ToASCII(base::StringPiece16(value));
+    // Headers are ISO Latin 1.
+    const std::string& header_name = name.latin1();
+    const std::string& header_value = value.latin1();
     CHECK(header_name.find('\0') == std::string::npos);
     CHECK(header_value.find('\0') == std::string::npos);
     headers_->insert(ServiceWorkerHeaderMap::value_type(