Adds window resizing

Adds window resizing

I need to constrain sizes more, but this is a good start.
Also, it looks like resizing doesn't actually work. I suspect that is
a bug in NativeWidgetMus (or WindowTreeHostMojo). Will figure that out
separately.

This adds the new test suite, but no bots are running it yet. I'll
update the build files separately.

BUG=548420
TEST=none
R=ben@chromium.org

Committed: https://crrev.com/b6cb43b07ff48ffdd0467e12ce7e0256b822cace
Cr-Commit-Position: refs/heads/master@{#357000}

[Ben Goodger (Google), 2015-10-29 23:58:20]

lgtm

[sky, 2015-10-30 00:01:25]

The CQ bit was checked by sky@chromium.org

[commit-bot: I haz the power, 2015-10-30 00:04:14]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1416453005/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1416453005/1

[commit-bot: I haz the power, 2015-10-30 00:43:34]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-10-30 00:44:19]

Patchset 1 (id:??) landed as
https://crrev.com/b6cb43b07ff48ffdd0467e12ce7e0256b822cace
Cr-Commit-Position: refs/heads/master@{#357000}