Reduce flickers of Injection

The injection dynamic data was loaded in the background and then post to
main thread to update UI. However, it usually updates after
Fragement.onResume(), which causes the flicker.

To make it more smooth, DashboardFragment to wait for the dynamic data
observers to update UI for a short period, which eliminates the flicker
in most cases.

Also skip the repeated tiles refresh called by onCategoriesChanged in
onResume after all preferences refreshed.

Test: robotest, visual
Bug: 229177114
Change-Id: I04650af9692703f1fc1e6e5ad2090f051b1eeb81