fix(checkbox): Fix native checked is not true when MdCheckbox initial checked value is true (#2055)

* Fix checked is not true when MdCheckbox initial checked value is true

* Add test

* fix lint

Author: tinayuangao

src/lib/checkbox/checkbox.spec.ts

@@ -100,6 +100,15 @@ describe('MdCheckbox', () => {
       expect(inputElement.indeterminate).toBe(false);
     });
 
+    it('should change native element checked when check programmatically', () => {
+      expect(inputElement.checked).toBe(false);
+
+      checkboxInstance.checked = true;
+      fixture.detectChanges();
+
+      expect(inputElement.checked).toBe(true);
+    });
+
     it('should toggle checked state on click', () => {
       expect(checkboxInstance.checked).toBe(false);
 

src/lib/checkbox/checkbox.ts

@@ -1,4 +1,5 @@
 import {
+    ChangeDetectorRef,
     ChangeDetectionStrategy,
     Component,
     ElementRef,
@@ -156,7 +157,9 @@ export class MdCheckbox implements ControlValueAccessor {
 
   hasFocus: boolean = false;
 
-  constructor(private _renderer: Renderer, private _elementRef: ElementRef) {
+  constructor(private _renderer: Renderer,
+              private _elementRef: ElementRef,
+              private _changeDetectorRef: ChangeDetectorRef) {
     this.color = 'accent';
   }
 
@@ -174,6 +177,7 @@ export class MdCheckbox implements ControlValueAccessor {
       this._checked = checked;
       this._transitionCheckState(
           this._checked ? TransitionCheckState.Checked : TransitionCheckState.Unchecked);
+      this._changeDetectorRef.markForCheck();
     }
   }