Bar chart shows blank view during loading state

We'd expect that bar chart can show blank view
during loading state.

If user doesn't change its loading state, preference
draws view directly.

But if user changes its loading state to true explicitly,
if means bar chart needs to take some time to load
data. So, we won't initialize view now.

Once the state is updated to false, we will start to
initialize view again.

Test: visual, robotest
Bug: 123539793
Change-Id: I5fc9e5a48e49c43ade6fd5a4dc7ba3458cf7c07d