rAc multi-login support

This CL should have no effective change, it's only a change in code to get us closer to supporting multiple users. I've verified that all of this code works with the one change of passing along all the usernames to the account chooser model rather than just the first one.

As there will be some more work required on the view side as well as the server side (probably), this is as good a point as any to stop.

The current problem on the server side is that our passive login flow (sort of) only works for a single user. Multiple users can get passively logged in, but if some do and some do not require passive sign in, we don't handle it well.

BUG=259543

Review URL: https://codereview.chromium.org/25549004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@228046 0039d316-1c4b-4281-b951-d872f2087c98
Import Mac cursor images from Blink repo

These images were only used by Chromium, never Blink itself, so this patch
simply puts them closer to where they're referenced.

I've added the list of imported files to the already-existing LICENSE block
in README.txt. Files are identical to their Blink versions except for
alias_cursor.png, on which I used pngcrush in order to create a valid PNG file.

BUG=303964

Review URL: https://codereview.chromium.org/25842004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@228047 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 228046
SkBitmap implementation using DRM buffers

BUG=

Review URL: https://codereview.chromium.org/26290006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@228048 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 228048