Remove unmodifiable map wrappers that could instead use UnmodifiableMapView.

sdk/lib/io/http_headers.dart

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 part of dart.io;
 
 class _HttpHeaders implements HttpHeaders {
   final Map<String, List<String>> _headers;
   final String protocolVersion;
 
@@ skipping 505 matching lines @@
     if (values != null) {
       values.forEach((headerValue) => parseCookieString(headerValue));
     }
     return cookies;
   }
 }
 
 
 class _HeaderValue implements HeaderValue {
   String _value;
-  _UnmodifiableMap<String, String> _parameters;
+  Map<String, String> _parameters;
+  Map<String, String> _unmodifiableParameters;
 
   _HeaderValue([String this._value = "", Map<String, String> parameters]) {
     if (parameters != null) {
-      _parameters =
-          new _UnmodifiableMap(new HashMap<String, String>.from(parameters));
+      _parameters = new HashMap<String, String>.from(parameters);
     }
   }
 
   static _HeaderValue parse(String value,
                             {parameterSeparator: ";",
                              preserveBackslash: false}) {
     // Parse the string.
     var result = new _HeaderValue();
     result._parse(value, parameterSeparator, preserveBackslash);
     return result;
   }
 
   String get value => _value;
 
   void _ensureParameters() {
     if (_parameters == null) {
-      _parameters = new _UnmodifiableMap(new HashMap<String, String>());
+      _parameters = new HashMap<String, String>();
     }
   }
 
   Map<String, String> get parameters {
     _ensureParameters();
-    return _parameters;
+    if (_unmodifiableParameters == null) {
+      _unmodifiableParameters = new UnmodifiableMapView(_parameters);
+    }
+    return _unmodifiableParameters;
   }
 
   String toString() {
     StringBuffer sb = new StringBuffer();
     sb.write(_value);
     if (parameters != null && parameters.length > 0) {
       _parameters.forEach((String name, String value) {
         sb..write("; ")..write(name)..write("=")..write(value);
       });
     }
@@ skipping 29 matching lines @@
       }
       index++;
     }
 
     void maybeExpect(String expected) {
       if (s[index] == expected) index++;
     }
 
     void parseParameters() {
       var parameters = new HashMap<String, String>();
-      _parameters = new _UnmodifiableMap(parameters);
+      _parameters = new UnmodifiableMapView(parameters);
 
       String parseParameterName() {
         int start = index;
         while (!done()) {
           if (s[index] == " " || s[index] == "\t" || s[index] == "=") break;
           index++;
         }
         return s.substring(start, index).toLowerCase();
       }
 
@@ skipping 58 matching lines @@
                String subType,
                String charset,
                Map<String, String> parameters)
       : _primaryType = primaryType, _subType = subType, super("") {
     if (_primaryType == null) _primaryType = "";
     if (_subType == null) _subType = "";
     _value = "$_primaryType/$_subType";
     if (parameters != null) {
       _ensureParameters();
       parameters.forEach((String key, String value) {
-        this._parameters._map[key.toLowerCase()] = value.toLowerCase();
+        this._parameters[key.toLowerCase()] = value.toLowerCase();
       });
     }
     if (charset != null) {
       _ensureParameters();
-      this._parameters._map["charset"] = charset.toLowerCase();
+      this._parameters["charset"] = charset.toLowerCase();
     }
   }
 
   _ContentType._();
 
   static _ContentType parse(String value) {
     var result = new _ContentType._();
     result._parse(value, ";", false);
     int index = result._value.indexOf("/");
     if (index == -1 || index == (result._value.length - 1)) {
@@ skipping 162 matching lines @@
             (codeUnit >= 0x23 && codeUnit <= 0x2B) ||
             (codeUnit >= 0x2D && codeUnit <= 0x3A) ||
             (codeUnit >= 0x3C && codeUnit <= 0x5B) ||
             (codeUnit >= 0x5D && codeUnit <= 0x7E))) {
         throw new FormatException(
             "Invalid character in cookie value, code unit: '$codeUnit'");
       }
     }
   }
 }
-
-
-class _UnmodifiableMap<K, V> implements Map<K, V> {
-  final Map _map;
-  const _UnmodifiableMap(this._map);
-
-  bool containsValue(Object value) => _map.containsValue(value);
-  bool containsKey(Object key) => _map.containsKey(key);
-  V operator [](Object key) => _map[key];
-  void operator []=(K key, V value) {
-    throw new UnsupportedError("Cannot modify an unmodifiable map");
-  }
-  V putIfAbsent(K key, V ifAbsent()) {
-    throw new UnsupportedError("Cannot modify an unmodifiable map");
-  }
-  addAll(Map other) {
-    throw new UnsupportedError("Cannot modify an unmodifiable map");
-  }
-  V remove(Object key) {
-    throw new UnsupportedError("Cannot modify an unmodifiable map");
-  }
-  void clear() {
-    throw new UnsupportedError("Cannot modify an unmodifiable map");
-  }
-  void forEach(void f(K key, V value)) => _map.forEach(f);
-  Iterable<K> get keys => _map.keys;
-  Iterable<V> get values => _map.values;
-  int get length => _map.length;
-  bool get isEmpty => _map.isEmpty;
-  bool get isNotEmpty => _map.isNotEmpty;
-}