Fix Z-order for a bubble when it appears for inactive window.

ui/views/widget/desktop_aura/desktop_window_tree_host_x11.cc

Index: ui/views/widget/desktop_aura/desktop_window_tree_host_x11.cc
diff --git a/ui/views/widget/desktop_aura/desktop_window_tree_host_x11.cc b/ui/views/widget/desktop_aura/desktop_window_tree_host_x11.cc
index 4a8f64cf47c459156b59e1f75e802b312897b433..a8215cb17f4930655e84f437feb7138692edf2ad 100644
--- a/ui/views/widget/desktop_aura/desktop_window_tree_host_x11.cc
+++ b/ui/views/widget/desktop_aura/desktop_window_tree_host_x11.cc
@@ -128,6 +128,25 @@ const char* kAtomsToCache[] = {
 const char kX11WindowRolePopup[] = "popup";
 const char kX11WindowRoleBubble[] = "bubble";
 
+// Returns the whole path from |window| to the root.
+std::vector<::Window> GetParentsList(XDisplay* xdisplay, ::Window window) {
+  ::Window parent_win, root_win;
+  Window* child_windows;
+  unsigned int num_child_windows;
+  std::vector<::Window> result;
+
+  while (window) {
+    result.push_back(window);
+    if (!XQueryTree(xdisplay, window,
+                    &root_win, &parent_win, &child_windows, &num_child_windows))
+      break;
+    if (child_windows)
+      XFree(child_windows);
+    window = parent_win;
+  }
+  return result;
+}
+
 }  // namespace
 
 ////////////////////////////////////////////////////////////////////////////////
@@ -415,6 +434,37 @@ void DesktopWindowTreeHostX11::SetSize(const gfx::Size& requested_size) {
   }
 }
 
+void DesktopWindowTreeHostX11::StackAbove(aura::Window* window) {
+  if (window && window->GetRootWindow()) {
+    ::Window window_below = window->GetHost()->GetAcceleratedWidget();
+    // Find all parent windows up to the root.
+    std::vector<::Window> window_below_parents =
+        GetParentsList(xdisplay_, window_below);
+    std::vector<::Window> window_above_parents =
+        GetParentsList(xdisplay_, xwindow_);
+
+    // Find their common ancestor.
+    auto it_below_window = window_below_parents.rbegin();
+    auto it_above_window = window_above_parents.rbegin();
+    for (; it_below_window != window_below_parents.rend() &&
+           it_above_window != window_above_parents.rend() &&
+           *it_below_window == *it_above_window;
+         ++it_below_window, ++it_above_window) {
+    }
+
+    if (it_below_window != window_below_parents.rend() &&
+        it_above_window != window_above_parents.rend()) {
+      // First stack |xwindow_| below so Z-order of |window| stays the same.
+      ::Window windows[] = {*it_below_window, *it_above_window};
+      if (XRestackWindows(xdisplay_, windows, 2) == 0) {
+        // Now stack them properly.
+        std::swap(windows[0], windows[1]);
+        XRestackWindows(xdisplay_, windows, 2);
+      }
+    }
+  }
+}
+
 void DesktopWindowTreeHostX11::StackAtTop() {
   XRaiseWindow(xdisplay_, xwindow_);
 }