Remove unmodifiable map wrappers that could instead use UnmodifiableMapView.

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..587910647ff75b068daa602e067346fe9b821291 100644
--- a/sdk/lib/io/http_headers.dart
+++ b/sdk/lib/io/http_headers.dart
@@ -523,12 +523,12 @@ class _HttpHeaders implements HttpHeaders {
 
 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);
     }
   }
 
@@ -545,13 +545,16 @@ class _HeaderValue implements HeaderValue {
 
   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() {
@@ -601,7 +604,7 @@ class _HeaderValue implements HeaderValue {
 
     void parseParameters() {
       var parameters = new HashMap<String, String>();
-      _parameters = new _UnmodifiableMap(parameters);
+      _parameters = new UnmodifiableMapView(parameters);
 
       String parseParameterName() {
         int start = index;
@@ -680,12 +683,12 @@ class _ContentType extends _HeaderValue implements ContentType {
     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();
     }
   }
 
@@ -868,34 +871,3 @@ class _Cookie implements Cookie {
     }
   }
 }
-
-
-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;
-}