Bug 860438 - Simplify JSContext handling {Cancel,Suspend,Resume}WorkersForWindow. r=gabor

The only functional difference here is the removal of a bug in which we were
constructing a dom::workers::AutoSafeJSContext around aCx, but then continuing
to pass aCx to the callee. If aCx were to be null, we'd end up with a mismatch
between the stack and the active cx. But it looks likes stuff depends on cx
being non-null anyway, so that probably never happened.

dom/base/nsGlobalWindow.cpp

@@ -1423,8 +1423,10 @@ nsGlobalWindow::FreeInnerObjects()
   NotifyDOMWindowDestroyed(this);
 
   // Kill all of the workers for this window.
+  // We push a cx so that exceptions get reported in the right DOM Window.
   nsIScriptContext *scx = GetContextInternal();
-  AutoPushJSContext cx(scx ? scx->GetNativeContext() : nullptr);
+  AutoPushJSContext cx(scx ? scx->GetNativeContext() : nsContentUtils::GetSafeJSContext());
+  JSAutoRequest ar(cx);
   mozilla::dom::workers::CancelWorkersForWindow(cx, this);
 
   // Close all offline storages for this window.
@@ -11018,8 +11020,10 @@ nsGlobalWindow::SuspendTimeouts(uint32_t aIncrease,
     DisableGamepadUpdates();
 
     // Suspend all of the workers for this window.
+  // We push a cx so that exceptions get reported in the right DOM Window.
     nsIScriptContext *scx = GetContextInternal();
-    AutoPushJSContext cx(scx ? scx->GetNativeContext() : nullptr);
+    AutoPushJSContext cx(scx ? scx->GetNativeContext() : nsContentUtils::GetSafeJSContext());
+    JSAutoRequest ar(cx);
     mozilla::dom::workers::SuspendWorkersForWindow(cx, this);
 
     TimeStamp now = TimeStamp::Now();
@@ -11109,8 +11113,10 @@ nsGlobalWindow::ResumeTimeouts(bool aThawChildren)
     }
 
     // Resume all of the workers for this window.
+    // We push a cx so that exceptions get reported in the right DOM Window.
     nsIScriptContext *scx = GetContextInternal();
-    AutoPushJSContext cx(scx ? scx->GetNativeContext() : nullptr);
+    AutoPushJSContext cx(scx ? scx->GetNativeContext() : nsContentUtils::GetSafeJSContext());
+    JSAutoRequest ar(cx);
     mozilla::dom::workers::ResumeWorkersForWindow(cx, this);
 
     // Restore all of the timeouts, using the stored time remaining

dom/workers/RuntimeService.cpp

@@ -1284,7 +1284,6 @@ RuntimeService::CancelWorkersForWindow(JSContext* aCx,
   GetWorkersForWindow(aWindow, workers);
 
   if (!workers.IsEmpty()) {
-    AutoSafeJSContext cx(aCx);
     for (uint32_t index = 0; index < workers.Length(); index++) {
       if (!workers[index]->Cancel(aCx)) {
         NS_WARNING("Failed to cancel worker!");
@@ -1303,7 +1302,6 @@ RuntimeService::SuspendWorkersForWindow(JSContext* aCx,
   GetWorkersForWindow(aWindow, workers);
 
   if (!workers.IsEmpty()) {
-    AutoSafeJSContext cx(aCx);
     for (uint32_t index = 0; index < workers.Length(); index++) {
       if (!workers[index]->Suspend(aCx)) {
         NS_WARNING("Failed to cancel worker!");
@@ -1322,7 +1320,6 @@ RuntimeService::ResumeWorkersForWindow(JSContext* aCx,
   GetWorkersForWindow(aWindow, workers);
 
   if (!workers.IsEmpty()) {
-    AutoSafeJSContext cx(aCx);
     for (uint32_t index = 0; index < workers.Length(); index++) {
       if (!workers[index]->Resume(aCx)) {
         NS_WARNING("Failed to cancel worker!");