feat(http): add basic http service

This implementation only works in JavaScript, while the Observable transpilation
story gets worked out. Right now, the service just makes a simple request,
and returns an Observable of Response.

Additional functionality will be captured in separate issues.

Fixes #2028

modules/angular2/src/http/headers.ts

@@ -0,0 +1,79 @@
+import {
+  isPresent,
+  isBlank,
+  isJsObject,
+  isType,
+  StringWrapper,
+  BaseException
+} from 'angular2/src/facade/lang';
+import {
+  isListLikeIterable,
+  List,
+  Map,
+  MapWrapper,
+  ListWrapper
+} from 'angular2/src/facade/collection';
+
+// (@jeffbcross): This is implemented mostly to spec, except that the entries method has been
+// removed because it doesn't exist in dart, and it doesn't seem worth adding it to the facade.
+
+export class Headers {
+  _headersMap: Map<string, List<string>>;
+  constructor(headers?: Headers | Object) {
+    if (isBlank(headers)) {
+      this._headersMap = MapWrapper.create();
+      return;
+    }
+
+    if (isPresent((<Headers>headers)._headersMap)) {
+      this._headersMap = (<Headers>headers)._headersMap;
+    } else if (isJsObject(headers)) {
+      this._headersMap = MapWrapper.createFromStringMap(headers);
+      MapWrapper.forEach(this._headersMap, (v, k) => {
+        if (!isListLikeIterable(v)) {
+          var list = ListWrapper.create();
+          ListWrapper.push(list, v);
+          MapWrapper.set(this._headersMap, k, list);
+        }
+      });
+    }
+  }
+
+  append(name: string, value: string): void {
+    var list = MapWrapper.get(this._headersMap, name) || ListWrapper.create();
+    ListWrapper.push(list, value);
+    MapWrapper.set(this._headersMap, name, list);
+  }
+
+  delete (name: string): void { MapWrapper.delete(this._headersMap, name); }
+
+  forEach(fn: Function) { return MapWrapper.forEach(this._headersMap, fn); }
+
+  get(header: string): string {
+    return ListWrapper.first(MapWrapper.get(this._headersMap, header));
+  }
+
+  has(header: string) { return MapWrapper.contains(this._headersMap, header); }
+
+  keys() { return MapWrapper.keys(this._headersMap); }
+
+  // TODO: this implementation seems wrong. create list then check if it's iterable?
+  set(header: string, value: string | List<string>): void {
+    var list = ListWrapper.create();
+    if (!isListLikeIterable(value)) {
+      ListWrapper.push(list, value);
+    } else {
+      ListWrapper.push(list, ListWrapper.toString((<List<string>>value)));
+    }
+
+    MapWrapper.set(this._headersMap, header, list);
+  }
+
+  values() { return MapWrapper.values(this._headersMap); }
+
+  getAll(header: string): Array<string> {
+    return MapWrapper.get(this._headersMap, header) || ListWrapper.create();
+  }
+
+  entries() { throw new BaseException('"entries" method is not implemented on Headers class'); }
+}