Revert "Remove unmodifiable map wrappers that could instead use UnmodifiableMapView."

sdk/lib/_internal/lib/js_mirrors.dart

Index: sdk/lib/_internal/lib/js_mirrors.dart
diff --git a/sdk/lib/_internal/lib/js_mirrors.dart b/sdk/lib/_internal/lib/js_mirrors.dart
index b67e6b43f3e8be0fcb93a8e7a3512e99bb44bc17..1036bfdb25540a67d5e265feb3ca4b8c3aefdfed 100644
--- a/sdk/lib/_internal/lib/js_mirrors.dart
+++ b/sdk/lib/_internal/lib/js_mirrors.dart
@@ -7,8 +7,7 @@ library dart._js_mirrors;
 import 'dart:async';
 
 import 'dart:collection' show
-    UnmodifiableListView,
-    UnmodifiableMapView;
+    UnmodifiableListView;
 
 import 'dart:mirrors';
 
@@ -2836,6 +2835,45 @@ class NoSuchStaticMethodError extends Error implements NoSuchMethodError {
   }
 }
 
+// Copied from package "unmodifiable_collection".
+// TODO(14314): Move to dart:collection.
+class UnmodifiableMapView<K, V> implements Map<K, V> {
+  Map<K, V> _source;
+  UnmodifiableMapView(Map<K, V> source) : _source = source;
+
+  static void _throw() {
+    throw new UnsupportedError("Cannot modify an unmodifiable Map");
+  }
+
+  int get length => _source.length;
+
+  bool get isEmpty => _source.isEmpty;
+
+  bool get isNotEmpty => _source.isNotEmpty;
+
+  V operator [](K key) => _source[key];
+
+  bool containsKey(K key) => _source.containsKey(key);
+
+  bool containsValue(V value) => _source.containsValue(value);
+
+  void forEach(void f(K key, V value)) => _source.forEach(f);
+
+  Iterable<K> get keys => _source.keys;
+
+  Iterable<V> get values => _source.values;
+
+  void operator []=(K key, V value) => _throw();
+
+  V putIfAbsent(K key, V ifAbsent()) { _throw(); }
+
+  void addAll(Map<K, V> other) => _throw();
+
+  V remove(K key) { _throw(); }
+
+  void clear() => _throw();
+}
+
 Symbol getSymbol(String name, LibraryMirror library) {
   if (_isPublicSymbol(name)) {
     return new _symbol_dev.Symbol.validated(name);