feat(change detection): export SimpleChange

Closes #4337

modules/angular2/test/compiler/runtime_metadata_spec.ts

@@ -29,7 +29,8 @@ import {
   AfterContentInit,
   AfterContentChecked,
   AfterViewInit,
-  AfterViewChecked
+  AfterViewChecked,
+  SimpleChange
 } from 'angular2/core';
 
 import {TEST_BINDINGS} from './test_bindings';
@@ -115,7 +116,7 @@ class DirectiveWithoutModuleId {
 class ComponentWithEverything implements OnChanges,
     OnInit, DoCheck, OnDestroy, AfterContentInit, AfterContentChecked, AfterViewInit,
     AfterViewChecked {
-  onChanges(changes: StringMap<string, any>): void {}
+  onChanges(changes: StringMap<string, SimpleChange>): void {}
   onInit(): void {}
   doCheck(): void {}
   onDestroy(): void {}

modules/angular2/test/public_api_spec.ts

@@ -961,6 +961,12 @@ var NG_API = [
   'SlicePipe',
   'SlicePipe.supports()',
   'SlicePipe.transform()',
+  'SimpleChange',
+  'SimpleChange.currentValue',
+  'SimpleChange.currentValue=',
+  'SimpleChange.previousValue',
+  'SimpleChange.previousValue=',
+  'SimpleChange.isFirstChange()',
   'TemplateRef',
   'TemplateRef.elementRef',
   'TemplateRef.elementRef=',