cleanup: move DomAdapter from angular2/core into angular2/platform/common_dom

BREAKING CHANGE

Before

import {DomAdapter} from 'angular2/core';

After

import {DomAdapter} from 'angular2/platform/common_dom';

Closes #5370

modules/angular2/test/platform/bootstrap_spec.ts

@@ -17,7 +17,7 @@ import {bootstrap} from 'angular2/platform/browser';
 import {ApplicationRef} from 'angular2/src/core/application_ref';
 import {Component, Directive, View, OnDestroy, platform} from 'angular2/core';
 import {BROWSER_PROVIDERS, BROWSER_APP_PROVIDERS} from 'angular2/platform/browser';
-import {DOM} from 'angular2/src/core/dom/dom_adapter';
+import {DOM} from 'angular2/src/platform/dom/dom_adapter';
 import {DOCUMENT} from 'angular2/src/platform/dom/dom_tokens';
 import {PromiseWrapper} from 'angular2/src/facade/async';
 import {provide, Inject, Injector, PLATFORM_INITIALIZER, APP_INITIALIZER} from 'angular2/core';

modules/angular2/test/platform/browser/ruler_spec.ts

@@ -11,7 +11,7 @@ import {
 } from 'angular2/testing_internal';
 import {SpyElementRef, SpyDomAdapter} from '../../core/spies';
 
-import {DOM, DomAdapter} from 'angular2/src/core/dom/dom_adapter';
+import {DOM, DomAdapter} from 'angular2/src/platform/dom/dom_adapter';
 
 import {Ruler, Rectangle} from 'angular2/src/platform/browser/ruler';
 import {createRectangle} from './rectangle_mock';

modules/angular2/test/platform/browser/title_spec.ts

@@ -1,5 +1,5 @@
 import {ddescribe, describe, it, iit, xit, expect, afterEach} from 'angular2/testing_internal';
-import {DOM} from 'angular2/src/core/dom/dom_adapter';
+import {DOM} from 'angular2/src/platform/dom/dom_adapter';
 import {Title} from 'angular2/platform/browser';
 
 export function main() {