[ozone] Remove temporary workaround to gpu cursor starting on main thread.
[ozone] Remove temporary workaround to gpu cursor starting on main thread.

After https://codereview.chromium.org/860073002/, we no longer need to
worry about race conditions resulting from messages arriving on main
thread before the filter is installed.

BUG=

Review URL: https://codereview.chromium.org/857233003

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#312461}

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