Bug 1584492 [Linux] Add mIsPIPWindow to nsWindow, r=jhorak

Depends on D47409

Differential Revision: https://phabricator.services.mozilla.com/D47410

--HG--
extra : moz-landing-system : lando

widget/gtk/nsWindow.cpp

@@ -472,6 +472,7 @@ nsWindow::nsWindow() {
   mTitlebarBackdropState = false;
 
   mHasAlphaVisual = false;
+  mIsPIPWindow = false;
 }
 
 nsWindow::~nsWindow() {
@@ -3651,6 +3652,8 @@ nsresult nsWindow::Create(nsIWidget* aParent, nsNativeWidget aNativeParent,
     }
   }
 
+  mIsPIPWindow = aInitData && aInitData->mPIPWindow;
+
   // ok, create our windows
   switch (mWindowType) {
     case eWindowType_dialog:

widget/gtk/nsWindow.h

@@ -276,6 +276,7 @@ class nsWindow final : public nsBaseWidget {
   nsIFrame* GetFrame();
   bool IsDestroyed() { return mIsDestroyed; }
   bool IsWaylandPopup();
+  bool IsPIPWindow() { return mIsPIPWindow; };
 
   void DispatchDragEvent(mozilla::EventMessage aMsg,
                          const LayoutDeviceIntPoint& aRefPoint, guint aTime);
@@ -523,6 +524,8 @@ class nsWindow final : public nsBaseWidget {
   bool mTitlebarBackdropState;
   // Draggable titlebar region maintained by UpdateWindowDraggingRegion
   LayoutDeviceIntRegion mDraggableRegion;
+  // It's PictureInPicture window.
+  bool mIsPIPWindow;
 
 #ifdef ACCESSIBILITY
   RefPtr<mozilla::a11y::Accessible> mRootAccessible;