Add DCHECKS() for current thread in ChildProcessLauncher
Add DCHECKS() for current thread in ChildProcessLauncher

And rename some functions to indicate when they don't run
on the default (client) thread.

This avoids misuse and makes it more obvious what threads we are on
given that this involves multiple threads (launcher thread, and
different client threads for renderers and other children - former
calls from UI thread, the latter from IO thread -
plus there are some Android quirks).

BUG=469248

Review URL: https://codereview.chromium.org/1002853003

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#321648}

hgl888/chromium-crosswalk,TheTypoMaster/chromium-crosswalk,Chilledheart/chromium,Pluto-tv/chromium-crosswalk,chuan9/chromium-crosswalk,ltilve/chromium,Pluto-tv/chromium-crosswalk,Just-D/chromium-1,fujunwei/chromium-crosswalk,chuan9/chromium-crosswalk,Just-D/chromium-1,ltilve/chromium,chuan9/chromium-crosswalk,TheTypoMaster/chromium-crosswalk,PeterWangIntel/chromium-crosswalk,Chilledheart/chromium,PeterWangIntel/chromium-crosswalk,Pluto-tv/chromium-crosswalk,fujunwei/chromium-crosswalk,axinging/chromium-crosswalk,ltilve/chromium,axinging/chromium-crosswalk,Fireblend/chromium-crosswalk,axinging/chromium-crosswalk,fujunwei/chromium-crosswalk,PeterWangIntel/chromium-crosswalk,Chilledheart/chromium,Fireblend/chromium-crosswalk,ltilve/chromium,hgl888/chromium-crosswalk,Fireblend/chromium-crosswalk,Fireblend/chromium-crosswalk,axinging/chromium-crosswalk,PeterWangIntel/chromium-crosswalk,ltilve/chromium,TheTypoMaster/chromium-crosswalk,chuan9/chromium-crosswalk,PeterWangIntel/chromium-crosswalk,Chilledheart/chromium,hgl888/chromium-crosswalk,hgl888/chromium-crosswalk,Pluto-tv/chromium-crosswalk,hgl888/chromium-crosswalk,Just-D/chromium-1,fujunwei/chromium-crosswalk,Just-D/chromium-1,PeterWangIntel/chromium-crosswalk,TheTypoMaster/chromium-crosswalk,chuan9/chromium-crosswalk,PeterWangIntel/chromium-crosswalk,TheTypoMaster/chromium-crosswalk,fujunwei/chromium-crosswalk,TheTypoMaster/chromium-crosswalk,Fireblend/chromium-crosswalk,Just-D/chromium-1,Just-D/chromium-1,Chilledheart/chromium,Fireblend/chromium-crosswalk,Just-D/chromium-1,axinging/chromium-crosswalk,PeterWangIntel/chromium-crosswalk,TheTypoMaster/chromium-crosswalk,hgl888/chromium-crosswalk,TheTypoMaster/chromium-crosswalk,PeterWangIntel/chromium-crosswalk,fujunwei/chromium-crosswalk,Pluto-tv/chromium-crosswalk,ltilve/chromium,hgl888/chromium-crosswalk,Fireblend/chromium-crosswalk,ltilve/chromium,axinging/chromium-crosswalk,ltilve/chromium,fujunwei/chromium-crosswalk,Pluto-tv/chromium-crosswalk,hgl888/chromium-crosswalk,axinging/chromium-crosswalk,chuan9/chromium-crosswalk,Fireblend/chromium-crosswalk,Pluto-tv/chromium-crosswalk,Chilledheart/chromium,Chilledheart/chromium,Fireblend/chromium-crosswalk,chuan9/chromium-crosswalk,Chilledheart/chromium,Pluto-tv/chromium-crosswalk,Just-D/chromium-1,axinging/chromium-crosswalk,Pluto-tv/chromium-crosswalk,axinging/chromium-crosswalk,fujunwei/chromium-crosswalk,axinging/chromium-crosswalk,Just-D/chromium-1,ltilve/chromium,Chilledheart/chromium,chuan9/chromium-crosswalk,hgl888/chromium-crosswalk,fujunwei/chromium-crosswalk,axinging/chromium-crosswalk,chuan9/chromium-crosswalk,TheTypoMaster/chromium-crosswalk