Bug 939049 - Part 2: Add generic ComputeLength code for backends with no such functionality. r=jrmuizel
Bug 939601 - Refactor current thread assert into helper.  r=cpearce
Bug 939569 - Part 1: Stop using #pragma once in webspeech code; r=smaug
Bug 939569 - Part 2: Build layout/build in unified mode; r=glandium