fix: refactor the MutationObserver token to not break AoT

Author: crisbeto

src/lib/core/observe-content/observe-content.spec.ts

@@ -1,6 +1,6 @@
 import {Component} from '@angular/core';
 import {async, TestBed, ComponentFixture, fakeAsync, tick} from '@angular/core/testing';
-import {ObserveContentModule} from './observe-content';
+import {ObserveContentModule, MdMutationObserverFactory} from './observe-content';
 
 /**
  * TODO(elad): `ProxyZone` doesn't seem to capture the events raised by
@@ -63,14 +63,16 @@ describe('Observe content', () => {
         imports: [ObserveContentModule],
         declarations: [ComponentWithDebouncedListener],
         providers: [{
-          provide: MutationObserver,
-          useValue: function(callback: Function) {
-            callbacks.push(callback);
-
-            return {
-              observe: () => {},
-              disconnect: () => {}
-            };
+          provide: MdMutationObserverFactory,
+          useValue: {
+            create: function(callback: Function) {
+              callbacks.push(callback);
+
+              return {
+                observe: () => {},
+                disconnect: () => {}
+              };
+            }
           }
         }]
       });

src/lib/core/observe-content/observe-content.ts

@@ -8,11 +8,22 @@ import {
   EventEmitter,
   OnDestroy,
   AfterContentInit,
-  Injector,
+  Injectable,
 } from '@angular/core';
 import {Subject} from 'rxjs/Subject';
 import 'rxjs/add/operator/debounceTime';
 
+/**
+ * Factory that creates a new MutationObserver and allows us to stub it out in unit tests.
+ * @docs-private
+ */
+@Injectable()
+export class MdMutationObserverFactory {
+  create(callback): MutationObserver {
+    return new MutationObserver(callback);
+  }
+}
+
 /**
  * Directive that triggers a callback whenever the content of
  * its associated element has changed.
@@ -32,15 +43,18 @@ export class ObserveContent implements AfterContentInit, OnDestroy {
   /** Debounce interval for emitting the changes. */
   @Input() debounce: number;
 
-  constructor(private _elementRef: ElementRef, private _injector: Injector) { }
+  constructor(
+    private _mutationObserverFactory: MdMutationObserverFactory,
+    private _elementRef: ElementRef) { }
 
   ngAfterContentInit() {
     this._debouncer
       .debounceTime(this.debounce)
       .subscribe(mutations => this.event.emit(mutations));
 
-    this._observer = new (this._injector.get(MutationObserver) as any)(
-        (mutations: MutationRecord[]) => this._debouncer.next(mutations));
+    this._observer = this._mutationObserverFactory.create((mutations: MutationRecord[]) => {
+      this._debouncer.next(mutations);
+    });
 
     this._observer.observe(this._elementRef.nativeElement, {
       characterData: true,
@@ -57,13 +71,11 @@ export class ObserveContent implements AfterContentInit, OnDestroy {
   }
 }
 
+
 @NgModule({
   exports: [ObserveContent],
   declarations: [ObserveContent],
-  providers: [
-    // Pass the MutationObserver through DI so it can be stubbed when testing.
-    { provide: MutationObserver, useValue: MutationObserver }
-  ]
+  providers: [MdMutationObserverFactory]
 })
 export class ObserveContentModule {
   /** @deprecated */