Dart DOM: Add Element attributes setter

BUG=None
TEST=None

Review URL: https://chromereviews.googleplex.com/3526016

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge/dart@143 260f80e4-7a28-3924-810f-c04153c831b5

client/html/src/Element.dart

@@ -76,6 +76,7 @@ interface Element extends Node /*, common.NodeSelector, common.ElementTraversal
   Element.tag(String tag);
 
   Map<String, String> get attributes();
+  void set attributes(Map<String, String> value);
 
   ElementList get elements();
 

client/html/src/ElementWrappingImplementation.dart

@@ -401,11 +401,23 @@ class ElementWrappingImplementation extends NodeWrappingImplementation implement
 
   ElementWrappingImplementation._wrap(ptr) : super._wrap(ptr);
 
+  ElementAttributeMap _elementAttributeMap;
   _CssClassSet _cssClassSet;
   _DataAttributeMap _dataAttributes;
 
   Map<String, String> get attributes() {
-    return new ElementAttributeMap._wrap(_ptr);
+    if (_elementAttributeMap === null) {
+      _elementAttributeMap = new ElementAttributeMap._wrap(_ptr);
+    }
+    return _elementAttributeMap;
+  }
+
+  void set attributes(Map<String, String> value) {
+    Map<String, String> attributes = this.attributes;
+    attributes.clear();
+    for (String key in value.getKeys()) {
+      attributes[key] = value[key];
+    }
   }
 
   ElementList get elements() => new _ChildrenElementList._wrap(_ptr);