Fix ResolverDrawerLayout child measurement

ResoverDrawerLayout didn't take into account its horizontal paddints
when measured its children.
Plus a trivial refactoring.

Fix: 223775954
Test: Manual test: open Chooser in landscape mode on a phone with
3-button navigation.

Change-Id: Ia4835a2ddb52bff4ba36597dea3a3d7bf83967aa