I saw something similar happening after I unnested the folders in the referenced CL. But the error went away for reasons I don't know. Maybe moving things back into subfolders fixes the problem?

Ok, after some debugging, my tldr is __import__ is a buggy method, don't use it.

We have been using this method forever, though the fact that this bug only triggered now is a big redflag. I guess there is some sort of short circuting logic that make __import__ only type check fromlist argument if importing module_name matches certain condition.

Now stepping back, I believe the reason we need to add fromlist argument is to make sure that we import the module by name, not the top level package. 

"When the name variable is of the form package.module, normally, the top-level package (the name up till the first dot) is returned, not the module named by name. However, when a non-empty fromlist argument is given, the module named by name is returned.
" (https://docs.python.org/2/library/functions.html)

To fix this, I use https://docs.python.org/2/library/importlib.html#importlib.import_module which import the module directly.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/d15c79924126a8ed94ac652fcd4c760347d142d6

commit d15c79924126a8ed94ac652fcd4c760347d142d6
Author: catapult-deps-roller@chromium.org <catapult-deps-roller@chromium.org>
Date: Sat Sep 16 01:32:18 2017

Roll src/third_party/catapult/ 5c13bd84f..c49949828 (3 commits)

https://chromium.googlesource.com/external/github.com/catapult-project/catapult.git/+log/5c13bd84fb39..c49949828b72

$ git log 5c13bd84f..c49949828 --date=short --no-merges --format='%ad %ae %s'
2017-09-15 nednguyen [common] Update discover.py to use importlib for importing module instead of builtin __import__
2017-09-15 charliea Disable power monitoring on all desktop platforms
2017-09-15 bpastene devil: Fix args help text of video_recorder.py

Created with:
  roll-dep src/third_party/catapult
BUG= 765783 ,765383


Documentation for the AutoRoller is here:
https://skia.googlesource.com/buildbot/+/master/autoroll/README.md

If the roll is causing failures, see:
http://www.chromium.org/developers/tree-sheriffs/sheriff-details-chromium#TOC-Failures-due-to-DEPS-rolls


CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.android:android_optional_gpu_tests_rel
TBR=sullivan@chromium.org

Change-Id: I948184a41bc8572be7266d2c176c03ef49562381
Reviewed-on: https://chromium-review.googlesource.com/669684
Reviewed-by: <catapult-deps-roller@chromium.org>
Commit-Queue: <catapult-deps-roller@chromium.org>
Cr-Commit-Position: refs/heads/master@{#502465}
[modify] https://crrev.com/d15c79924126a8ed94ac652fcd4c760347d142d6/DEPS