The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/4138b8862b533cba8a7d8efb5afe10f2bc90f52b

commit 4138b8862b533cba8a7d8efb5afe10f2bc90f52b
Author: Daniel Bratell <bratell@opera.com>
Date: Thu Nov 23 17:57:09 2017

Let jumbo ignore known strange files in sources lists

Many targets end up with stray files in their sources list,
files which trigger no toolchain. Jumbo used to assert that this
was bad but since other tools handle it silently, jumbo
should also be a bit more forgiving.

Bug:  787836 
Change-Id: Ib70c3c5a053621de656af15fb4fcc413673db93c
Reviewed-on: https://chromium-review.googlesource.com/785811
Reviewed-by: Bruce Dawson <brucedawson@chromium.org>
Commit-Queue: Daniel Bratell <bratell@opera.com>
Cr-Commit-Position: refs/heads/master@{#518979}
[modify] https://crrev.com/4138b8862b533cba8a7d8efb5afe10f2bc90f52b/build/config/merge_for_jumbo.py

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/6e004f6a753bbf3480974058f4c549e93a2babfc

commit 6e004f6a753bbf3480974058f4c549e93a2babfc
Author: Daniel Bratell <bratell@opera.com>
Date: Fri Dec 08 07:10:30 2017

[jumbo] Ignore some more file types people put in sources lists

*.js and *.css files (used in //extensions) are not dangerous
to have in sources lists so silently let them be.

Bug:  787836 
Change-Id: I8dc2c16505594ed5342cad008dc1ca8b5a499b73
Reviewed-on: https://chromium-review.googlesource.com/814554
Reviewed-by: Bruce Dawson <brucedawson@chromium.org>
Commit-Queue: Daniel Bratell <bratell@opera.com>
Cr-Commit-Position: refs/heads/master@{#522731}
[modify] https://crrev.com/6e004f6a753bbf3480974058f4c549e93a2babfc/build/config/merge_for_jumbo.py

I think no more changes is needed short term here so closing as Fixed.