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

- Bug 1191491 - Do not dispatch an audio-playback notification when swapping browsers; r=smaug (dacb2ff694)
- Bug 1192252 - Add a helper RAII class for managing the cleanup in nsFrameLoader::SwapWithOtherLoader; r=smaug (362488db65)

docshell/base/nsDocShell.h

@@ -262,6 +262,12 @@ public:
   // is no longer applied
   void NotifyAsyncPanZoomStopped();
 
+  void SetInFrameSwap(bool aInSwap)
+  {
+    mInFrameSwap = aInSwap;
+  }
+  bool InFrameSwap();
+
 private:
   // An observed docshell wrapper is created when recording markers is enabled.
   mozilla::UniquePtr<mozilla::ObservedDocShell> mObserved;
@@ -910,6 +916,7 @@ protected:
   bool mUseRemoteTabs;
   bool mDeviceSizeIsPageSize;
   bool mWindowDraggingAllowed;
+  bool mInFrameSwap;
 
   // Because scriptability depends on the mAllowJavascript values of our
   // ancestors, we cache the effective scriptability and recompute it when