Fix a flicker problem on top app bar

The height of top app bar area is dependent on the line count of title.
This mechanism is always triggered when entering either subsetting page
or rotating the screen, regardless the state of collapsing toolbar. That
is saying this mechanism caused a flicker problem or a title in wrong
color. The mechanism will be updated to check the state of collapsing
toolbar to make sure that it is only triggered if the collapsing toolbar
is in expanded state.

This changes also added null checker to app bar since there's no
AppBarLayout existing in the older version of Android.

Fix: 186419089
Fix: 187709056
Fix: 191746368
Test: visual verified
1) Navigate to a subsetting page with multiline title
2) Rotate the screen to landscape mode and collapse the title
3) Rotate the screen to portrait mode and see if the title is in
collapsing state

Change-Id: Ica868245e0b0a799f76b7f953c606c8e543375f6