import changes from `dev' branch of rmottola/Arctic-Fox:

- Bug 1199289 - r=valentin,dao (bfaf064b19)
- Bug 1202312 - Remove an old forward declaration and typedef. r=kats (1fc905fe5d)
- Bug 1170894 - Implement nsIFrameLoader::SwitchProcessAndLoadURI. r=smaug (194b0e81f6)
- Bug 1199765 - Add support to TabParent for querying the active state of remote browsers. r=Mossop (a9b24d4083)
- Bug 1165796 - Part 1: Make PrefEnabledRunnable usable for other preference names. r=baku (2e83d3ecc7)
- Bug 1168933 - Send referrer when downloading worker script. r=khuey (69e48dea42)
- Bug 1165796 - Part 2: Implement PerformanceObserver.r=baku (9f16f01051)
- Bug 1165796 - Part 0: Unified build fix. r=baku (0605bf4397)
- Bug 1165796 - Part 3: Fix PerformanceObserverEntryList::GetEntries filtering for initiatorType. r=baku (12d07cee20)
- Bug 1192787 - Readd performance enabled test to ResponseEndHighRes; r=baku (f75fbaba13)
- Bug 1197003 - Part 1 - PerformanceObserver::Disconenct() should be called before mPerformance is destroyed. r=baku (d4dd3a960b)
- Bug 1195700 - Disconnect performance observer before being destroyed to avoid crash. r=baku (e9e743d4d2)
- Bug 1197003 - Part 2 - Implement processing algorithm for PerformanceObserver to notify a batch of entries. r=baku (4a0432765f)
- Bug 1155761 followup: Annotate nsPerformance::InsertUserEntry as 'override'. rs=ehsan (0552b7f75f)

dom/base/nsFrameLoader.cpp

@@ -273,6 +273,42 @@ nsFrameLoader::LoadURI(nsIURI* aURI)
   return rv;
 }
 
+NS_IMETHODIMP
+nsFrameLoader::SwitchProcessAndLoadURI(nsIURI* aURI)
+{
+  nsCOMPtr<nsIURI> URIToLoad = aURI;
+  nsRefPtr<TabParent> tp = nullptr;
+
+  MutableTabContext context;
+  nsCOMPtr<mozIApplication> ownApp = GetOwnApp();
+  nsCOMPtr<mozIApplication> containingApp = GetContainingApp();
+
+  bool tabContextUpdated = true;
+  if (ownApp) {
+    tabContextUpdated = context.SetTabContextForAppFrame(ownApp, containingApp);
+  } else if (OwnerIsBrowserFrame()) {
+    // The |else| above is unnecessary; OwnerIsBrowserFrame() implies !ownApp.
+    tabContextUpdated = context.SetTabContextForBrowserFrame(containingApp);
+  } else {
+    tabContextUpdated = context.SetTabContextForNormalFrame();
+  }
+  NS_ENSURE_STATE(tabContextUpdated);
+
+  nsCOMPtr<Element> ownerElement = mOwnerContent;
+  tp = ContentParent::CreateBrowserOrApp(context, ownerElement, nullptr);
+  if (!tp) {
+    return NS_ERROR_FAILURE;
+  }
+  mRemoteBrowserShown = false;
+
+  nsresult rv = SwapRemoteBrowser(tp);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+  LoadURI(URIToLoad);
+  return NS_OK;
+}
+
 NS_IMETHODIMP
 nsFrameLoader::SetIsPrerendered()
 {
@@ -2573,6 +2609,57 @@ nsFrameLoader::SetRemoteBrowser(nsITabParent* aTabParent)
   ShowRemoteFrame(ScreenIntSize(0, 0));
 }
 
+nsresult
+nsFrameLoader::SwapRemoteBrowser(nsITabParent* aTabParent)
+{
+  nsRefPtr<TabParent> newParent = TabParent::GetFrom(aTabParent);
+  if (!newParent || !mRemoteBrowser) {
+    return NS_ERROR_DOM_INVALID_STATE_ERR;
+  }
+  if (!IsRemoteFrame()) {
+    NS_WARNING("Switching from in-process to out-of-process is not supported.");
+    return NS_ERROR_NOT_IMPLEMENTED;
+  }
+  if (!OwnerIsBrowserOrAppFrame()) {
+    NS_WARNING("Switching process for non-mozbrowser/app frame is not supported.");
+    return NS_ERROR_NOT_IMPLEMENTED;
+  }
+  if (newParent == mRemoteBrowser) {
+    return NS_OK;
+  }
+  nsCOMPtr<nsIObserverService> os = services::GetObserverService();
+  if (os) {
+    os->NotifyObservers(NS_ISUPPORTS_CAST(nsIFrameLoader*, this),
+                        "frameloader-message-manager-will-change", nullptr);
+  }
+
+  mRemoteBrowser->CacheFrameLoader(nullptr);
+  mRemoteBrowser->SetOwnerElement(nullptr);
+  mRemoteBrowser->Detach();
+  mRemoteBrowser->Destroy();
+
+  if (mMessageManager) {
+    mMessageManager->Disconnect();
+    mMessageManager = nullptr;
+  }
+
+  mRemoteBrowser = newParent;
+  mRemoteBrowser->Attach(this);
+  mChildID = mRemoteBrowser->Manager()->ChildID();
+  ReallyLoadFrameScripts();
+  InitializeBrowserAPI();
+
+  if (os) {
+    os->NotifyObservers(NS_ISUPPORTS_CAST(nsIFrameLoader*, this),
+                        "frameloader-message-manager-changed", nullptr);
+  }
+  if (!mRemoteBrowserShown) {
+    ShowRemoteFrame(ScreenIntSize(0, 0));
+  }
+
+  return NS_OK;
+}
+
 void
 nsFrameLoader::SetDetachedSubdocFrame(nsIFrame* aDetachedFrame,
                                       nsIDocument* aContainerDoc)