Ignore fullscreen windows which are behind other windows for fullscreen mode.

chrome/browser/fullscreen_chromeos.cc

Index: chrome/browser/fullscreen_chromeos.cc
diff --git a/chrome/browser/fullscreen_chromeos.cc b/chrome/browser/fullscreen_chromeos.cc
index acdeb04f280b8255d401213d5537ecc7ca09b672..605f4bd49f8eca9855bc86ddea6d8b9a40fb4f75 100644
--- a/chrome/browser/fullscreen_chromeos.cc
+++ b/chrome/browser/fullscreen_chromeos.cc
@@ -11,5 +11,5 @@ bool IsFullScreenMode() {
   // and fix if necessary.
   ash::internal::RootWindowController* controller =
       ash::internal::RootWindowController::ForTargetRootWindow();
-  return controller && controller->GetTopmostFullscreenWindow();
+  return controller && controller->GetWindowForFullscreenMode();
 }