Issue #1587 Part 12 (followup 2): Allow clearing of signal by setting to null.

dom/fetch/FetchDriver.cpp

@@ -499,6 +499,11 @@ FetchDriver::OnStartRequest(nsIRequest* aRequest,
     return rv;
   }
 
+  if (!mChannel) {
+    MOZ_ASSERT(!mObserver);
+    return NS_BINDING_ABORTED;
+  }
+
   // We should only get to the following code once.
   MOZ_ASSERT(!mPipeOutputStream);
   MOZ_ASSERT(mObserver);

dom/fetch/Request.cpp

@@ -425,7 +425,7 @@ Request::Constructor(const GlobalObject& aGlobal,
   }
 
   if (aInit.mSignal.WasPassed()) {
-    signal = &aInit.mSignal.Value();
+    signal = aInit.mSignal.Value();
   }
 
   if (NS_IsMainThread()) {

dom/webidl/Request.webidl

@@ -53,7 +53,7 @@ dictionary RequestInit {
   DOMString integrity;
 
   [Func="AbortController::IsEnabled"]
-  AbortSignal signal;
+  AbortSignal? signal;
 
   [Func="FetchObserver::IsEnabled"]
   ObserverCallback observe;