BMP-in-ICO should respect alpha in Windows V3 32bpp RGB bitmaps.

Confirmed with Firefox source code and some vague Wikipedia references, as well
as IE's behavior on a test image.

BUG=38618
TEST=none
TBR=senorblanco

Review URL: https://codereview.chromium.org/279433002

git-svn-id: svn://svn.chromium.org/blink/trunk@173567 bbb929c8-8fbe-4397-9dbb-9b2b20218538