Bug 1703953 - Part 3: Apply mozilla/use-isInstance to devtools r=julienw

Differential Revision: https://phabricator.services.mozilla.com/D142068

devtools/client/performance-new/@types/gecko.d.ts

@@ -486,3 +486,11 @@ declare interface XULElementWithCommandHandler {
 }
 
 declare type nsIPrefBranch = MockedExports.nsIPrefBranch;
+
+// chrome context-only DOM isInstance method
+// XXX: This hackishly extends Function because there is no way to extend DOM constructors.
+// Callers should manually narrow the type when needed.
+// See also https://github.com/microsoft/TypeScript-DOM-lib-generator/issues/222
+interface Function {
+  isInstance(obj: any): boolean;
+}

devtools/client/performance-new/symbolication.jsm.js

@@ -139,7 +139,7 @@ async function getResultFromWorker(workerURL, initialMessageToWorker) {
     worker.onerror = errorEvent => {
       gActiveWorkers.delete(worker);
       worker.terminate();
-      if (errorEvent instanceof ErrorEvent) {
+      if (ErrorEvent.isInstance(errorEvent)) {
         const { message, filename, lineno } = errorEvent;
         const error = new Error(`${message} at ${filename}:${lineno}`);
         error.name = "WorkerError";
@@ -152,17 +152,10 @@ async function getResultFromWorker(workerURL, initialMessageToWorker) {
     // Handle errors from messages that cannot be deserialized. I'm not sure
     // how to get into such a state, but having this handler seems like a good
     // idea.
-    worker.onmessageerror = errorEvent => {
+    worker.onmessageerror = () => {
       gActiveWorkers.delete(worker);
       worker.terminate();
-      if (errorEvent instanceof ErrorEvent) {
-        const { message, filename, lineno } = errorEvent;
-        const error = new Error(`${message} at ${filename}:${lineno}`);
-        error.name = "WorkerMessageError";
-        reject(error);
-      } else {
-        reject(new Error("Error in worker"));
-      }
+      reject(new Error("Error in worker"));
     };
 
     worker.postMessage(initialMessageToWorker);