feat(dart/transform): Add directiveMetadata{To,From}Map

Add utility methods to convert `render.dom.DirectiveMetadata` to and
from maps. This will allow saving and restoring `DirectiveMetadata` in
the Angular 2 Transformer.

We discussed adding this as a member on `DirectiveMetadata`. Since this
is not necessary for anything except the Transformer, we decided to put
it into a separate file to avoid shipping it with the Angular 2 core
code.

modules/angular2/src/render/dom/convert.js

@@ -0,0 +1,47 @@
+import {ListWrapper, MapWrapper} from 'angular2/src/facade/collection';
+import {isPresent} from 'angular2/src/facade/lang';
+import {DirectiveMetadata} from 'angular2/src/render/api';
+
+/**
+ * Converts a [DirectiveMetadata] to a map representation. This creates a copy,
+ * that is, subsequent changes to `meta` will not be mirrored in the map.
+ */
+export function directiveMetadataToMap(meta: DirectiveMetadata): Map {
+  return MapWrapper.createFromPairs([
+    ['id', meta.id],
+    ['selector', meta.selector],
+    ['compileChildren', meta.compileChildren],
+    ['hostListeners', _cloneIfPresent(meta.hostListeners)],
+    ['hostProperties', _cloneIfPresent(meta.hostProperties)],
+    ['properties', _cloneIfPresent(meta.properties)],
+    ['readAttributes', _cloneIfPresent(meta.readAttributes)],
+    ['type', meta.type],
+    ['version', 1]
+  ]);
+}
+
+/**
+ * Converts a map representation of [DirectiveMetadata] into a
+ * [DirectiveMetadata] object. This creates a copy, that is, subsequent changes
+ * to `map` will not be mirrored in the [DirectiveMetadata] object.
+ */
+export function directiveMetadataFromMap(map: Map): DirectiveMetadata {
+  return new DirectiveMetadata({
+    id: MapWrapper.get(map, 'id'),
+    selector: MapWrapper.get(map, 'selector'),
+    compileChildren: MapWrapper.get(map, 'compileChildren'),
+    hostListeners: _cloneIfPresent(MapWrapper.get(map, 'hostListeners')),
+    hostProperties: _cloneIfPresent(MapWrapper.get(map, 'hostProperties')),
+    properties: _cloneIfPresent(MapWrapper.get(map, 'properties')),
+    readAttributes: _cloneIfPresent(MapWrapper.get(map, 'readAttributes')),
+    type: MapWrapper.get(map, 'type')
+  });
+}
+
+/**
+ * Clones the [List] or [Map] `o` if it is present.
+ */
+function _cloneIfPresent(o) {
+  if (!isPresent(o)) return null;
+  return ListWrapper.isList(o) ? ListWrapper.clone(o) : MapWrapper.clone(o);
+}