ui: Turn on slimming paint by default with impl-side painting.
ui: Turn on slimming paint by default with impl-side painting.

Slimming paint is now much faster than PicturePile backed recording
for impl-side painting. It's what we're going to ship when we enable
impl-side, so make it the default. Left the disable switch just in case
to try out PicturePile if we need to for some reason until we turn
on impl-side by default.

R=piman@chromium.org, sky
BUG=466426

Review URL: https://codereview.chromium.org/1141583003

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#329469}

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