fix(input): properly determine input value

Right now the `MdInputDirective` tries to cache the `value` of the input.

To do this, the `MdInputDirective` needs to listen for `NgControl` value changes and for native `(change)` events.

This will be problematic when a value is set directly to the input element (using `[value]` property binding) because Angular is only able to recognize this change in the first ChangeDetection.

```html
<md-input-container>
  <input md-input [value]="myValue" placeholder="Label">
</md-input-container>
```

The approach of updating the value in the `ngAfterViewInit` lifecycle hook, will result in a binding change while being in a ChangeDetection, which leads to a ChangeDetection error.

```
Expression has changed after it was checked. Previous value: 'true'. Current value: 'false'.
```

Fixes angular#2441. Fixes angular#2363

src/lib/input/input-container.spec.ts

@@ -1,9 +1,9 @@
 import {async, TestBed, inject} from '@angular/core/testing';
 import {Component} from '@angular/core';
-import {FormsModule, ReactiveFormsModule} from '@angular/forms';
+import {FormsModule, ReactiveFormsModule, FormControl} from '@angular/forms';
 import {By} from '@angular/platform-browser';
 import {MdInputModule} from './input';
-import {MdInputContainer} from './input-container';
+import {MdInputContainer, MdInputDirective} from './input-container';
 import {Platform} from '../core/platform/platform';
 import {PlatformModule} from '../core/platform/index';
 import {
@@ -41,6 +41,8 @@ describe('MdInputContainer', function () {
         MdInputContainerZeroTestController,
         MdTextareaWithBindings,
         MdInputContainerWithDisabled,
+        MdInputContainerWithValueBinding,
+        MdInputContainerWithFormControl,
         MdInputContainerMissingMdInputTestController
       ],
     });
@@ -128,6 +130,20 @@ describe('MdInputContainer', function () {
     expect(el.classList.contains('md-empty')).toBe(false, 'should not be empty');
   }));
 
+  it('should not be empty when the value set before view init', async(() => {
+    let fixture = TestBed.createComponent(MdInputContainerWithValueBinding);
+    fixture.detectChanges();
+
+    let placeholderEl = fixture.debugElement.query(By.css('.md-input-placeholder')).nativeElement;
+
+    expect(placeholderEl.classList).not.toContain('md-empty');
+
+    fixture.componentInstance.value = '';
+    fixture.detectChanges();
+
+    expect(placeholderEl.classList).toContain('md-empty');
+  }));
+
   it('should not treat the number 0 as empty', async(() => {
     let fixture = TestBed.createComponent(MdInputContainerZeroTestController);
     fixture.detectChanges();
@@ -141,6 +157,20 @@ describe('MdInputContainer', function () {
     });
   }));
 
+  it('should update the value when using FormControl.setValue', () => {
+    let fixture = TestBed.createComponent(MdInputContainerWithFormControl);
+    fixture.detectChanges();
+
+    let input = fixture.debugElement.query(By.directive(MdInputDirective))
+      .injector.get(MdInputDirective) as MdInputDirective;
+
+    expect(input.value).toBeFalsy();
+
+    fixture.componentInstance.formControl.setValue('something');
+
+    expect(input.value).toBe('something');
+  });
+
   it('should add id', () => {
     let fixture = TestBed.createComponent(MdInputContainerTextTestController);
     fixture.detectChanges();
@@ -326,6 +356,13 @@ class MdInputContainerPlaceholderElementTestComponent {
   placeholder: string = 'Default Placeholder';
 }
 
+@Component({
+  template: `<md-input-container><input md-input [formControl]="formControl"></md-input-container>`
+})
+class MdInputContainerWithFormControl {
+  formControl = new FormControl();
+}
+
 @Component({
   template: `<md-input-container><input md-input [placeholder]="placeholder"></md-input-container>`
 })
@@ -429,6 +466,16 @@ class MdInputContainerZeroTestController {
   value = 0;
 }
 
+@Component({
+  template: `
+    <md-input-container>
+      <input md-input placeholder="Label" [value]="value">
+    </md-input-container>`
+})
+class MdInputContainerWithValueBinding {
+  value: string = 'Initial';
+}
+
 @Component({
   template: `
     <md-input-container>

src/lib/input/input-container.ts

@@ -74,10 +74,10 @@ export class MdHint {
     '[id]': 'id',
     '(blur)': '_onBlur()',
     '(focus)': '_onFocus()',
-    '(input)': '_onInput()',
   }
 })
-export class MdInputDirective implements AfterContentInit {
+export class MdInputDirective {
+
   /** Whether the element is disabled. */
   @Input()
   get disabled() { return this._disabled; }
@@ -116,8 +116,9 @@ export class MdInputDirective implements AfterContentInit {
   }
   private _type = 'text';
 
-  /** The element's value. */
-  value: any;
+  /** The input element's value. */
+  get value() { return this._elementRef.nativeElement.value; }
+  set value(value: string) { this._elementRef.nativeElement.value = value; }
 
   /**
    * Emits an event when the placeholder changes so that the `md-input-container` can re-validate.
@@ -143,18 +144,9 @@ export class MdInputDirective implements AfterContentInit {
   constructor(private _elementRef: ElementRef,
               private _renderer: Renderer,
               @Optional() public _ngControl: NgControl) {
+
     // Force setter to be called in case id was not specified.
     this.id = this.id;
-
-    if (this._ngControl && this._ngControl.valueChanges) {
-      this._ngControl.valueChanges.subscribe((value) => {
-        this.value = value;
-      });
-    }
-  }
-
-  ngAfterContentInit() {
-    this.value = this._elementRef.nativeElement.value;
   }
 
   /** Focuses the input element. */
@@ -164,8 +156,6 @@ export class MdInputDirective implements AfterContentInit {
 
   _onBlur() { this.focused = false; }
 
-  _onInput() { this.value = this._elementRef.nativeElement.value; }
-
   /** Make sure the input is a supported type. */
   private _validateType() {
     if (MD_INPUT_INVALID_TYPES.indexOf(this._type) != -1) {