build: fix error with latest MDC canary version (#20540)

Updates an object to match the signature from the latest MDC Canary version.

Author: crisbeto

package.json

@@ -61,7 +61,7 @@
     "@types/youtube": "^0.0.38",
     "@webcomponents/custom-elements": "^1.1.0",
     "core-js": "^2.6.9",
-    "material-components-web": "8.0.0-canary.911014711.0",
+    "material-components-web": "8.0.0-canary.85a1fa9ea.0",
     "rxjs": "^6.5.3",
     "rxjs-tslint-rules": "^4.33.1",
     "systemjs": "0.19.43",

src/material-experimental/mdc-slider/slider.ts

@@ -256,6 +256,8 @@ export class MatSlider implements AfterViewInit, OnChanges, OnDestroy, ControlVa
     registerWindowEventHandler: () => {},
     deregisterWindowEventHandler: () => {},
     removeTrackActiveStyleProperty: (_propertyName: string) => {},
+    emitDragStartEvent: (_value: number, _thumb: Thumb) => {},
+    emitDragEndEvent: (_value: number, _thumb: Thumb) => {}
   };
 
   /** Instance of the MDC slider foundation for this slider. */