Bug 1635196 - Make sure GetSymbolTableMozPromise promise is always fulfilled - r=mstange

In rare cases, a dispatch may fail (e.g., threads are shutting down), we should handle this failure by rejecting the promise on the spot.

Depends on D73791

Differential Revision: https://phabricator.services.mozilla.com/D73792

tools/profiler/gecko/nsProfiler.cpp

@@ -870,7 +870,7 @@ RefPtr<nsProfiler::SymbolTablePromise> nsProfiler::GetSymbolTableMozPromise(
     }
   }
 
-  mSymbolTableThread->Dispatch(NS_NewRunnableFunction(
+  nsresult rv = mSymbolTableThread->Dispatch(NS_NewRunnableFunction(
       "nsProfiler::GetSymbolTableMozPromise runnable on ProfSymbolTable thread",
       [promiseHolder = std::move(promiseHolder),
        debugPath = nsCString(aDebugPath),
@@ -887,6 +887,12 @@ RefPtr<nsProfiler::SymbolTablePromise> nsProfiler::GetSymbolTableMozPromise(
         }
       }));
 
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    // Get-symbol task was not dispatched and therefore won't fulfill the
+    // promise, we must reject the promise now.
+    promiseHolder.Reject(NS_ERROR_FAILURE, __func__);
+  }
+
   return promise;
 }