Backed out changeset 7f9088d3354d (bug 1807838) for causing bc failur…

…es on browser_modal_resize.js. CLOSED TREE

xpfe/appshell/AppWindow.cpp

@@ -2228,18 +2228,11 @@ nsresult AppWindow::SetRootShellSize(int32_t aWidth, int32_t aHeight) {
 
 NS_IMETHODIMP AppWindow::SizeShellTo(nsIDocShellTreeItem* aShellItem,
                                      int32_t aCX, int32_t aCY) {
-  MOZ_ASSERT(aShellItem == mDocShell || aShellItem == mPrimaryContentShell);
-  if (aShellItem == mDocShell) {
-    auto newSize =
-        LayoutDeviceIntSize(aCX, aCY) + GetOuterToInnerSizeDifference(mWindow);
-    SetSize(newSize.width, newSize.height, /* aRepaint = */ true);
-    return NS_OK;
-  }
-
   // XXXTAB This is wrong, we should actually reflow based on the passed in
   // shell.  For now we are hacking and doing delta sizing.  This is bad
   // because it assumes all size we add will go to the shell which probably
   // won't happen.
+
   nsCOMPtr<nsIBaseWindow> shellAsWin(do_QueryInterface(aShellItem));
   NS_ENSURE_TRUE(shellAsWin, NS_ERROR_FAILURE);
 
@@ -2628,6 +2621,11 @@ void AppWindow::IntrinsicallySizeShell(const CSSIntSize& aWindowDiff,
     return;
   }
   RefPtr<nsDocShell> docShell = mDocShell;
+  nsCOMPtr<nsIDocShellTreeOwner> treeOwner;
+  docShell->GetTreeOwner(getter_AddRefs(treeOwner));
+  if (!treeOwner) {
+    return;
+  }
 
   CSSIntCoord maxWidth = 0;
   CSSIntCoord maxHeight = 0;
@@ -2656,7 +2654,7 @@ void AppWindow::IntrinsicallySizeShell(const CSSIntSize& aWindowDiff,
 
   int32_t width = pc->CSSPixelsToDevPixels(size->width);
   int32_t height = pc->CSSPixelsToDevPixels(size->height);
-  SizeShellTo(docShell, width, height);
+  treeOwner->SizeShellTo(docShell, width, height);
 
   // Update specified size for the final LoadPositionFromXUL call.
   aSpecWidth = size->width + aWindowDiff.width;