feat(change_detection): uppercase and lowercase pipes

because the world needs more uppercase madness

[✔] clang-format
[✔] tests

modules/angular2/src/change_detection/pipes/lowercase_pipe.ts

@@ -0,0 +1,58 @@
+import {isString, StringWrapper} from 'angular2/src/facade/lang';
+import {Pipe} from './pipe';
+
+// HACK: workaround for Traceur behavior.
+// It expects all transpiled modules to contain this marker.
+// TODO: remove this when we no longer use traceur
+export var __esModule = true;
+
+/**
+ * Implements lowercase transforms to text.
+ *
+ * # Example
+ *
+ * In this example we transform the user text lowercase.
+ *
+ *  ```
+ * @Component({
+ *   selector: "username-cmp"
+ * })
+ * @View({
+ *  inline: "Username: {{ user | lowercase }}"
+ * })
+ * class Username {
+ *  user:string;
+ * }
+ *
+ * ```
+ *
+ * @exportedAs angular2/pipes
+ */
+export class LowerCasePipe extends Pipe {
+  _latestValue: string;
+  constructor() {
+    super();
+    this._latestValue = null;
+  }
+  supports(str): boolean { return isString(str); }
+
+  onDestroy(): void { this._latestValue = null; }
+
+  transform(value: string): string {
+    if (this._latestValue !== value) {
+      this._latestValue = value;
+      return StringWrapper.toLowerCase(value);
+    } else {
+      return this._latestValue;
+    }
+  }
+}
+
+/**
+ * @exportedAs angular2/pipes
+ */
+export class LowerCaseFactory {
+  supports(str): boolean { return isString(str); }
+
+  create(): Pipe { return new LowerCasePipe(); }
+}