Create a widget if necessary when auto hide flag is sent

Now the state change will change when frames arrives, we first
need to create widget if the auto hide is set in creation time.

BUG=751915
TEST=None

Change-Id: If8810692766a4c83f6f55de2bd9553fa1cd7ea0e
Reviewed-on: https://chromium-review.googlesource.com/599360
Commit-Queue: Mitsuru Oshima <oshima@chromium.org>
Reviewed-by: David Reveman <reveman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#491633}

components/exo/shell_surface.cc

@@ -462,6 +462,10 @@ void ShellSurface::SetPinned(ash::mojom::WindowPinType type) {
 void ShellSurface::SetSystemUiVisibility(bool autohide) {
   TRACE_EVENT1("exo", "ShellSurface::SetSystemUiVisibility", "autohide",
                autohide);
+
+  if (!widget_)
+    CreateShellSurfaceWidget(ui::SHOW_STATE_NORMAL);
+
   ash::wm::SetAutoHideShelf(widget_->GetNativeWindow(), autohide);
 }