feat(app-bar): Add isCollapsed() for checking collapsed state (#1230)

Returns whether or not the app bar is in a collapsed state.

- Adds `isCollapsed: boolean`

Author: trimox

demos/components/app-bar/app-bar-demo.html

@@ -55,6 +55,20 @@ <h2>Design & API Documentation</h2>
             </tr>
           </tbody>
         </table>
+        <table>
+          <thead>
+            <tr>
+              <th>Methods</th>
+              <th>Description</th>
+            </tr>
+          </thead>
+          <tbody>
+            <tr>
+              <td>isCollapsed: boolean</td>
+              <td>Whether or not the app bar is in a collapsed state.</td>
+            </tr>
+          </tbody>
+        </table>
         <table>
           <thead>
             <tr>

packages/app-bar/app-bar.ts

@@ -271,6 +271,11 @@ export class MdcAppBar implements AfterContentInit, AfterViewInit, OnDestroy {
     }
   }
 
+  isCollapsed(): boolean {
+    return this._getHostElement().classList.contains('mdc-top-app-bar--short-collapsed') ||
+      this._getHostElement().classList.contains('mdc-top-app-bar--short-collapsed');
+  }
+
   initializeFoundation(): void {
     setTimeout(() => {
       this._foundation.destroy();

test/app-bar/app-bar.test.ts

@@ -82,6 +82,7 @@ describe('MdcAppBar', () => {
       fixture.detectChanges();
       expect(testDebugElement.nativeElement.classList.contains('mdc-top-app-bar--fixed')).toBe(true);
       expect(testDebugElement.nativeElement.classList.contains('mdc-top-app-bar--short')).toBe(false);
+      expect(testInstance.isCollapsed()).toBe(false);
     });
   });
 });