Swtich from max_action_buttons resource to a method.

We want to limit the number of size thresholds that an application will
report. Instead of using a dimen resource that will increase the number
of thresholds, we calculate the max number of action buttons dynamically
in code.

Bug: 25394588
Change-Id: I8ece331cd02fb116b49734003cec112708d27f85