Note: It looks like not all of the icons on #41 got used in the end. The update_menu_severity icons all got combined into one.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/bf0c21d44b16d6e1a3c973ee5e94e4355ed4fe96

commit bf0c21d44b16d6e1a3c973ee5e94e4355ed4fe96
Author: spqchan <spqchan@chromium.org>
Date: Thu Jul 14 19:12:08 2016

[Material][Mac] Update App Menu Icons and Colors

Change the "Low Severity" color to Green. Update the icons to the MD
ones.

BUG= 624643 ,  626775 

Review-Url: https://codereview.chromium.org/2139573003
Cr-Commit-Position: refs/heads/master@{#405532}

[modify] https://crrev.com/bf0c21d44b16d6e1a3c973ee5e94e4355ed4fe96/chrome/browser/ui/cocoa/toolbar/app_toolbar_button.h
[modify] https://crrev.com/bf0c21d44b16d6e1a3c973ee5e94e4355ed4fe96/chrome/browser/ui/cocoa/toolbar/app_toolbar_button.mm
[modify] https://crrev.com/bf0c21d44b16d6e1a3c973ee5e94e4355ed4fe96/chrome/browser/ui/cocoa/toolbar/toolbar_controller.mm