Add optimized _OneByteString.toLowerCase.

sdk/lib/io/http_headers.dart

Index: sdk/lib/io/http_headers.dart
diff --git a/sdk/lib/io/http_headers.dart b/sdk/lib/io/http_headers.dart
index 5dd5c55fd064e50f44e9c3e7d43047a2c3dc0518..50452b1ce345d5f93a41966499ab70cc87108565 100644
--- a/sdk/lib/io/http_headers.dart
+++ b/sdk/lib/io/http_headers.dart
@@ -28,10 +28,10 @@ class _HttpHeaders implements HttpHeaders {
     }
   }
 
-  List<String> operator[](String name) => _headers[name.toLowerCase()];
+  List<String> operator[](String name) => _headers[_ASCII.toLowerCase(name)];
 
   String value(String name) {
-    name = name.toLowerCase();
+    name = _ASCII.toLowerCase(name);
     List<String> values = _headers[name];
     if (values == null) return null;
     if (values.length > 1) {
@@ -42,7 +42,7 @@ class _HttpHeaders implements HttpHeaders {
 
   void add(String name, value) {
     _checkMutable();
-    _addAll(name.toLowerCase(), value);
+    _addAll(_ASCII.toLowerCase(name), value);
   }
 
   void _addAll(String name, value) {
@@ -55,14 +55,14 @@ class _HttpHeaders implements HttpHeaders {
 
   void set(String name, Object value) {
     _checkMutable();
-    name = name.toLowerCase();
+    name = _ASCII.toLowerCase(name);
     _headers.remove(name);
     _addAll(name, value);
   }
 
   void remove(String name, Object value) {
     _checkMutable();
-    name = name.toLowerCase();
+    name = _ASCII.toLowerCase(name);
     List<String> values = _headers[name];
     if (values != null) {
       int index = values.indexOf(value);
@@ -75,7 +75,7 @@ class _HttpHeaders implements HttpHeaders {
 
   void removeAll(String name) {
     _checkMutable();
-    name = name.toLowerCase();
+    name = _ASCII.toLowerCase(name);
     _headers.remove(name);
   }
 
@@ -329,7 +329,7 @@ class _HttpHeaders implements HttpHeaders {
         break;
 
       case HttpHeaders.CONNECTION:
-        var lowerCaseValue = value.toLowerCase();
+        var lowerCaseValue = _ASCII.toLowerCase(value);
         if (lowerCaseValue == 'close') {
           _persistentConnection = false;
         } else if (lowerCaseValue == 'keep-alive') {
@@ -361,7 +361,7 @@ class _HttpHeaders implements HttpHeaders {
   }
 
   void _set(String name, String value) {
-    assert(name == name.toLowerCase());
+    assert(name == _ASCII.toLowerCase(name));
     List<String> values = new List<String>();
     _headers[name] = values;
     values.add(value);