fix(tabs): tabs crashing on chrome under certain conditions

Prevents the tabs from either crashing Chrome (in Angular < 2.3) or throwing an animation error (in Angular >= 2.3). This was happening when the animations get triggered before the element is inserted into the DOM and thus doesn't have a computed `transform` value.

Fixes #2151.

Author: crisbeto

src/lib/tabs/tab-body.html

@@ -1,5 +1,5 @@
 <div class="md-tab-body-content" #content
-     [@translateTab]="_position"
+     [@translateTab]="_canBeAnimated ? _position : null"
      (@translateTab.start)="_onTranslateTabStarted($event)"
      (@translateTab.done)="_onTranslateTabComplete($event)">
   <template cdkPortalHost></template>

src/lib/tabs/tab-body.spec.ts

@@ -168,6 +168,20 @@ describe('MdTabBody', () => {
       expect(fixture.componentInstance.mdTabBody._portalHost.hasAttached()).toBe(false);
     }));
   });
+
+  it('it should toggle the canBeAnimated flag', () => {
+    let fixture: ComponentFixture<SimpleTabBodyApp>;
+    let tabBody: MdTabBody;
+
+    fixture = TestBed.createComponent(SimpleTabBodyApp);
+    tabBody = fixture.componentInstance.mdTabBody;
+
+    expect(tabBody._canBeAnimated).toBe(false);
+
+    fixture.detectChanges();
+
+    expect(tabBody._canBeAnimated).toBe(true);
+  });
 });
 
 

src/lib/tabs/tab-body.ts

@@ -12,7 +12,10 @@ import {
   transition,
   AnimationTransitionEvent,
   ElementRef,
-  Optional
+  Optional,
+  ChangeDetectorRef,
+  AfterViewChecked,
+  AfterContentChecked,
 } from '@angular/core';
 import {TemplatePortal, PortalHostDirective, Dir, LayoutDirection} from '../core';
 import 'rxjs/add/operator/map';
@@ -65,7 +68,7 @@ export type MdTabBodyOriginState = 'left' | 'right';
     ])
   ]
 })
-export class MdTabBody implements OnInit {
+export class MdTabBody implements OnInit, AfterViewChecked, AfterContentChecked {
   /** The portal host inside of this container into which the tab body content will be loaded. */
   @ViewChild(PortalHostDirective) _portalHost: PortalHostDirective;
 
@@ -92,6 +95,10 @@ export class MdTabBody implements OnInit {
     }
   }
 
+  /** Whether the element is allowed to be animated. */
+  _canBeAnimated: boolean = false;
+
+  /** The origin position from which this tab should appear when it is centered into view. */
   _origin: MdTabBodyOriginState;
 
   /** The origin position from which this tab should appear when it is centered into view. */
@@ -106,7 +113,10 @@ export class MdTabBody implements OnInit {
     }
   }
 
-  constructor(private _elementRef: ElementRef, @Optional() private _dir: Dir) {}
+  constructor(
+    @Optional() private _dir: Dir,
+    private _elementRef: ElementRef,
+    private _changeDetectorRef: ChangeDetectorRef) { }
 
   /**
    * After initialized, check if the content is centered and has an origin. If so, set the
@@ -128,6 +138,25 @@ export class MdTabBody implements OnInit {
     }
   }
 
+  /**
+   * After the content has been checked, determines whether the element should be allowed to
+   * animate. This has to be limited, because under a specific set of circumstances (see #2151),
+   * the animations can be triggered too early, which either crashes Chrome by putting it into an
+   * infinite loop (with Angular < 2.3.0) or throws an error because the element doesn't have a
+   * computed style (with Angular > 2.3.0). This can alternatively be determined by checking the
+   * transform: canBeAnimated = getComputedStyle(element) !== '', however document.contains should
+   * be faster since it doesn't cause a reflow.
+   */
+  ngAfterContentChecked() {
+    if (!this._canBeAnimated) {
+      this._canBeAnimated = document.contains(this._elementRef.nativeElement);
+
+      if (this._canBeAnimated) {
+        this._changeDetectorRef.markForCheck();
+      }
+    }
+  }
+
   _onTranslateTabStarted(e: AnimationTransitionEvent) {
     if (this._isCenterPosition(e.toState)) {
       this.onCentering.emit(this._elementRef.nativeElement.clientHeight);
@@ -151,7 +180,6 @@ export class MdTabBody implements OnInit {
     return this._dir && this._dir.value === 'rtl' ? 'rtl' : 'ltr';
   }
 
-
   /** Whether the provided position state is considered center, regardless of origin. */
   private _isCenterPosition(position: MdTabBodyPositionState|string): boolean {
     return position == 'center' ||