Bug 1142727 - Do not intercept sandboxed iframes with service workers; r=nsm

This is temporary until we clarify what we want to do with these
iframes in the spec.

docshell/base/nsDocShell.cpp

@@ -13950,6 +13950,11 @@ NS_IMETHODIMP
 nsDocShell::ShouldPrepareForIntercept(nsIURI* aURI, bool aIsNavigate, bool* aShouldIntercept)
 {
   *aShouldIntercept = false;
+  if (mSandboxFlags) {
+    // If we're sandboxed, don't intercept.
+    return NS_OK;
+  }
+
   nsCOMPtr<nsIServiceWorkerManager> swm = mozilla::services::GetServiceWorkerManager();
   if (!swm) {
     return NS_OK;