We use the following icon on Android, it's optimised for applying a masking colour. I guess you need a vector icon though?

https://cs.chromium.org/chromium/src/chrome/android/java/res/drawable-xxhdpi/ic_chrome.png?q=f:+ic_chrome+f:and&dr

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/0f3475f069c371804e7cd351194e15775d8e32a4

commit 0f3475f069c371804e7cd351194e15775d8e32a4
Author: Tetsui Ohkubo <tetsui@chromium.org>
Date: Thu Sep 28 01:47:38 2017

Add default icon to notification settings.

In notification settings, there was no defualt icon for notifier
without favicon. As a result, the notifier texts are not aligend.

Before: http://screen/Dm5RpJ42F98
After: http://screen/0tx8h9G9GPb

TEST=manual
BUG= 768736 

Change-Id: Id0e1ebc674c39acac63036bee7d1fa91f0817e86
Reviewed-on: https://chromium-review.googlesource.com/686086
Reviewed-by: James Cook <jamescook@chromium.org>
Commit-Queue: Tetsui Ohkubo <tetsui@chromium.org>
Cr-Commit-Position: refs/heads/master@{#504861}
[modify] https://crrev.com/0f3475f069c371804e7cd351194e15775d8e32a4/ash/message_center/notifier_settings_view.cc
[modify] https://crrev.com/0f3475f069c371804e7cd351194e15775d8e32a4/ash/message_center/notifier_settings_view.h