fix(upgrade): fallback to root ng2 injector when element is compiled outside the document (#8684)

Currently downgraded ng2 elements fail inside a ui-router view because they are unable
to require an ng2 Injector via the require attribute of the DDO, because ui-router compiles
its templates before they are inserted in a ui-view. This adds a "fallback" behavior if
a parent injector cannot be found to go to the root ng2 Injector.

modules/@angular/upgrade/src/constants.ts

@@ -12,4 +12,4 @@ export const NG1_INJECTOR = '$injector';
 export const NG1_PARSE = '$parse';
 export const NG1_TEMPLATE_CACHE = '$templateCache';
 export const NG1_TESTABILITY = '$$testability';
-export const REQUIRE_INJECTOR = '^' + NG2_INJECTOR;
+export const REQUIRE_INJECTOR = '?^' + NG2_INJECTOR;

modules/@angular/upgrade/src/downgrade_ng2_adapter.ts

@@ -42,7 +42,7 @@ export class DowngradeNg2ComponentAdapter {
     this.contentInsertionPoint = document.createComment('ng1 insertion point');
 
     this.componentRef =
-        this.componentFactory.create(childInjector, [[this.contentInsertionPoint]], '#' + this.id);
+        this.componentFactory.create(childInjector, [[this.contentInsertionPoint]], this.element[0]);
     this.changeDetector = this.componentRef.changeDetectorRef;
     this.component = this.componentRef.instance;
   }

modules/@angular/upgrade/src/upgrade_adapter.ts

@@ -540,8 +540,9 @@ interface ComponentFactoryRefMap {
 }
 
 function ng1ComponentDirective(info: ComponentInfo, idPrefix: string): Function {
-  (<any>directiveFactory).$inject = [NG2_COMPONENT_FACTORY_REF_MAP, NG1_PARSE];
-  function directiveFactory(componentFactoryRefMap: ComponentFactoryRefMap,
+  (<any>directiveFactory).$inject = [NG1_INJECTOR, NG2_COMPONENT_FACTORY_REF_MAP, NG1_PARSE];
+  function directiveFactory(ng1Injector: angular.IInjectorService,
+                            componentFactoryRefMap: ComponentFactoryRefMap,
                             parse: angular.IParseService): angular.IDirective {
     var componentFactory: ComponentFactory<any> = componentFactoryRefMap[info.selector];
     if (!componentFactory) throw new Error('Expecting ComponentFactory for: ' + info.selector);
@@ -553,6 +554,9 @@ function ng1ComponentDirective(info: ComponentInfo, idPrefix: string): Function
         post: (scope: angular.IScope, element: angular.IAugmentedJQuery, attrs: angular.IAttributes,
                parentInjector: any, transclude: angular.ITranscludeFunction): void => {
           var domElement = <any>element[0];
+          if (parentInjector === null) {
+            parentInjector = ng1Injector.get(NG2_INJECTOR);
+          }
           var facade =
               new DowngradeNg2ComponentAdapter(idPrefix + (idCount++), info, element, attrs, scope,
                                                <Injector>parentInjector, parse, componentFactory);