Also fixed a bug where progressive disclosure expand button is displayed
incorrectly when # of preference == threshold exactly.
Change-Id: I518687e374853ae8ab1c7e5337822492d6fd99ff
Fix: 36557600
Test: robotests
Insteads of inserting tile onto screen using absolute priority values,
now each page can have a placeholder preference, and at run time we will
add dynamic dashboard tiles to placeholder's place.
Bug: 32827787
Test: RunSettingsRoboTests
Change-Id: I1fe9e11dce4eb6fb4a9b56af05a2b8e5cdae00d2
