Fix white flash when opening incognito NTP
This specifies a different default background color when in incognito
mode in ThemeProvider::GetDefaultColor, matching the MD incognito NTP.
The previous (non-MD) incognito NTP uses an ever-so-slightly different
shade of gray, so that still has a barely-noticeable flash.
I've checked that this doesn't affect the regular or the guest mode
NTP, and that the incognito one works both with and without a theme.
BUG=21798
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:closure_compilation
Review-Url: https://codereview.chromium.org/2891983003
Cr-Commit-Position: refs/heads/master@{#473224}
2 files changed
