chore(tabs): revert workaround for angular < 2.3

Reverts a workaround that was preventing the tabs from crashing the user's browser in Angular < 2.3, due to an animations issue. This was introduced initially in #2411.

Author: crisbeto

src/lib/tabs/tab-body.html

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

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

@@ -170,19 +170,6 @@ describe('MdTabBody', () => {
     }));
   });
 
-  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

@@ -7,9 +7,7 @@ import {
   OnInit,
   ElementRef,
   Optional,
-  ChangeDetectorRef,
   AfterViewChecked,
-  AfterContentChecked,
 } from '@angular/core';
 import {
   trigger,
@@ -75,7 +73,7 @@ export type MdTabBodyOriginState = 'left' | 'right';
     ])
   ]
 })
-export class MdTabBody implements OnInit, AfterViewChecked, AfterContentChecked {
+export class MdTabBody implements OnInit, AfterViewChecked {
   /** The portal host inside of this container into which the tab body content will be loaded. */
   @ViewChild(PortalHostDirective) _portalHost: PortalHostDirective;
 
@@ -102,9 +100,6 @@ export class MdTabBody implements OnInit, AfterViewChecked, AfterContentChecked
     }
   }
 
-  /** 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;
 
@@ -120,10 +115,7 @@ export class MdTabBody implements OnInit, AfterViewChecked, AfterContentChecked
     }
   }
 
-  constructor(
-    @Optional() private _dir: Dir,
-    private _elementRef: ElementRef,
-    private _changeDetectorRef: ChangeDetectorRef) { }
+  constructor(@Optional() private _dir: Dir, private _elementRef: ElementRef) { }
 
   /**
    * After initialized, check if the content is centered and has an origin. If so, set the
@@ -145,28 +137,6 @@ export class MdTabBody implements OnInit, AfterViewChecked, AfterContentChecked
     }
   }
 
-  /**
-   * 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.
-   *
-   * TODO: This can safely be removed after we stop supporting Angular < 2.4.2. The fix landed via
-   * https://github.com/angular/angular/commit/21030e9a1cf30e8101399d8535ed72d847a23ba6
-   */
-  ngAfterContentChecked() {
-    if (!this._canBeAnimated) {
-      this._canBeAnimated = document.body.contains(this._elementRef.nativeElement);
-
-      if (this._canBeAnimated) {
-        this._changeDetectorRef.markForCheck();
-      }
-    }
-  }
-
   _onTranslateTabStarted(e: AnimationEvent) {
     if (this._isCenterPosition(e.toState)) {
       this.onCentering.emit(this._elementRef.nativeElement.clientHeight);