Fix crash when closing color chooser dialog on macos

For some reason, closing the color chooser dialog caused a crash on
macos. By using NSNotificationCenter instead of providing a delegate
the crash goes away. I got the idea for this from the comment about the
__target method already in the code.

R=kylixrd@chromium.org, mark@chromium.org

Bug: 931267
Change-Id: Ide35a455ff12decc9dd83b30c80b584ab376242b
Reviewed-on: https://chromium-review.googlesource.com/c/1469461
Commit-Queue: Mark Mentovai <mark@chromium.org>
Reviewed-by: Mark Mentovai <mark@chromium.org>
Reviewed-by: Allen Bauer <kylixrd@chromium.org>
Cr-Commit-Position: refs/heads/master@{#634232}
4 files changed