fix(material-experimental/mdc-progress-bar): check observer function (#…

…21986)

* fix(material-experimental/mdc-progress-bar): check observer function

* fix(material-experimental/mdc-progress-bar): use typeof

(cherry picked from commit cfd3bc8)

src/material-experimental/mdc-progress-bar/progress-bar.ts

@@ -102,8 +102,14 @@ export class MatProgressBar extends _MatProgressBarMixinBase implements AfterVie
 
       if (resizeObserverConstructor) {
         const observer = new resizeObserverConstructor(callback);
-        observer.observe(this._rootElement);
-        return observer;
+
+        // Internal client users found production errors where `observe` was not a function
+        // on the constructed `observer`. This should not happen, but adding this check for this
+        // edge case.
+        if (typeof observer.observe === 'function') {
+          observer.observe(this._rootElement);
+          return observer;
+        }
       }
 
       return null;