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/benchmarks/src/compiler/compiler_benchmark.ts

@@ -1,6 +1,6 @@
 import {bootstrap} from 'angular2/bootstrap';
 import {BrowserDomAdapter} from 'angular2/src/platform/browser/browser_adapter';
-import {DOM} from 'angular2/src/core/dom/dom_adapter';
+import {DOM} from 'angular2/src/platform/dom/dom_adapter';
 import {PromiseWrapper} from 'angular2/src/facade/async';
 import {ListWrapper, Map, MapWrapper} from 'angular2/src/facade/collection';
 import {DateWrapper, Type, print, isPresent} from 'angular2/src/facade/lang';

modules/benchmarks/src/largetable/largetable_benchmark.ts

@@ -1,4 +1,4 @@
-import {DOM} from 'angular2/src/core/dom/dom_adapter';
+import {DOM} from 'angular2/src/platform/dom/dom_adapter';
 import {window, document, gc} from 'angular2/src/facade/browser';
 import {
   getIntParameter,

modules/benchmarks/src/naive_infinite_scroll/app.ts

@@ -3,7 +3,7 @@ import {getIntParameter, bindAction} from 'angular2/src/testing/benchmark_util';
 import {TimerWrapper} from 'angular2/src/facade/async';
 import {ScrollAreaComponent} from './scroll_area';
 import {NgIf, NgFor} from 'angular2/common';
-import {DOM} from 'angular2/src/core/dom/dom_adapter';
+import {DOM} from 'angular2/src/platform/dom/dom_adapter';
 import {document} from 'angular2/src/facade/browser';
 
 import {Component, Directive, View} from 'angular2/angular2';

modules/benchmarks/src/static_tree/tree_benchmark.ts

@@ -14,7 +14,7 @@ import {ComponentRef_} from 'angular2/src/core/linker/dynamic_component_loader';
 import {ApplicationRef} from 'angular2/src/core/application_ref';
 import {reflector} from 'angular2/src/core/reflection/reflection';
 import {ReflectionCapabilities} from 'angular2/src/core/reflection/reflection_capabilities';
-import {DOM} from 'angular2/src/core/dom/dom_adapter';
+import {DOM} from 'angular2/src/platform/dom/dom_adapter';
 import {window, document, gc} from 'angular2/src/facade/browser';
 import {
   getIntParameter,

modules/benchmarks/src/tree/tree_benchmark.ts

@@ -12,7 +12,7 @@ import {
 import {NgIf} from 'angular2/common';
 
 import {ApplicationRef} from 'angular2/src/core/application_ref';
-import {DOM} from 'angular2/src/core/dom/dom_adapter';
+import {DOM} from 'angular2/src/platform/dom/dom_adapter';
 import {isPresent} from 'angular2/src/facade/lang';
 import {window, document, gc} from 'angular2/src/facade/browser';
 import {