Browser: fix incognito icons and preview thumbnail color

Change-Id: Ib4c5c0b95b63b439e39afede8c99134c91b7f724
(cherry picked from commit 3d7dd283a95c5ee333b74561c9161d380503128f)

Conflicts:
	res/drawable-hdpi/ic_incognito_dark.png
	res/drawable-mdpi/ic_incognito_dark.png
	res/drawable-xhdpi/ic_incognito_dark.png
	res/drawable-xxhdpi/ic_incognito_dark.png
	res/drawable-xxxhdpi/ic_incognito_dark.png