Bug 1508595 - Only set an intercept controller when needed. r=asuth

We only need to expose an intercept controller in SharedWorkers if we're on
the non-parent-intercept version of ServiceWorkers or if e10s is off.
nsDocShell already does this dance and we have to mirror it.

Differential Revision: https://phabricator.services.mozilla.com/D12490

docshell/base/nsDocShell.cpp

@@ -480,6 +480,8 @@ nsDocShell::Create(BrowsingContext* aBrowsingContext)
   // If parent intercept is not enabled then we must forward to
   // the network controller from docshell.  We also enable if we're
   // in the parent process in order to support non-e10s configurations.
+  // Note: This check is duplicated in SharedWorkerInterfaceRequestor's
+  // constructor.
   if (!ServiceWorkerParentInterceptEnabled() || XRE_IsParentProcess()) {
     ds->mInterceptController = new ServiceWorkerInterceptController();
   }

dom/workers/remoteworkers/RemoteWorkerChild.cpp

@@ -10,6 +10,7 @@
 #include "mozilla/dom/MessagePort.h"
 #include "mozilla/dom/RemoteWorkerTypes.h"
 #include "mozilla/dom/ServiceWorkerInterceptController.h"
+#include "mozilla/dom/ServiceWorkerUtils.h"
 #include "mozilla/dom/workerinternals/ScriptLoader.h"
 #include "mozilla/dom/WorkerError.h"
 #include "mozilla/dom/WorkerPrivate.h"
@@ -87,15 +88,19 @@ public:
   NS_DECL_ISUPPORTS
 
   SharedWorkerInterfaceRequestor()
-    : mSWController(new ServiceWorkerInterceptController())
-  {}
+  {
+    // This check must match the code nsDocShell::Create.
+    if (!ServiceWorkerParentInterceptEnabled() || XRE_IsParentProcess()) {
+      mSWController = new ServiceWorkerInterceptController();
+    }
+  }
 
   NS_IMETHOD
   GetInterface(const nsIID& aIID, void** aSink) override
   {
     MOZ_ASSERT(NS_IsMainThread());
 
-    if (aIID.Equals(NS_GET_IID(nsINetworkInterceptController))) {
+    if (mSWController && aIID.Equals(NS_GET_IID(nsINetworkInterceptController))) {
       // If asked for the network intercept controller, ask the outer requestor,
       // which could be the docshell.
       RefPtr<ServiceWorkerInterceptController> swController = mSWController;