Bug 1566986 - Make getSymbols an async function so that callers always get a promise and never a synchronous exception. r=gregtatum

Differential Revision: https://phabricator.services.mozilla.com/D44400

--HG--
extra : moz-landing-system : lando

devtools/client/performance-new/popup/background.jsm

@@ -63,7 +63,7 @@ function adjustState(newState) {
   }
 }
 
-function getSymbols(debugName, breakpadId) {
+async function getSymbols(debugName, breakpadId) {
   if (symbolCache.size === 0) {
     primeSymbolStore(Services.profiler.sharedLibraries);
   }