fix(cdk-observers): prevent attribute renaming in closure compilers advanced optimizations (#7894)

src/cdk/observers/observe-content.ts

@@ -75,9 +75,9 @@ export class CdkObserveContent implements AfterContentInit, OnDestroy {
 
     if (this._observer) {
       this._observer.observe(this._elementRef.nativeElement, {
-        characterData: true,
-        childList: true,
-        subtree: true
+        'characterData': true,
+        'childList': true,
+        'subtree': true
       });
     }
   }