Merge 175108 (for crbug.com/171096)

Merge 175108 (for crbug.com/171096)
> mac: Attempt to fix a startup perf regression caused by r174778
> 
> NOTRY=true
> BUG=167798, 168084
> TEST=Install https://chrome.google.com/webstore/detail/slinky-elegant/bmanlajnpdncmhfkiccmbgeocgbncfln?hl=en
> Look at new tab button in active and inactive windows. Also check the new tab
> button with the default theme. Look at startup perf graphs, should improve by
> ~1.8ms.
> 
> 
> Review URL: https://chromiumcodereview.appspot.com/11748026

TBR=thakis@chromium.org
Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=177865