Running //third_party/android_platform/development/scripts/stack is the trigger, which we do in stack symbolization.

Turns out it can also be generated by the pydeps logic at presubmit time. Uploading a patch for that, too.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/ab2fa1006465933f0735b392a925746639b422e5

commit ab2fa1006465933f0735b392a925746639b422e5
Author: John Budorick <jbudorick@chromium.org>
Date: Fri Oct 06 16:59:49 2017

Don't write bytecode when generating pydeps files.

Bug:  767620 
Change-Id: I33072a124e7b487aeb97dba2b0c57d1daf3ea980
Reviewed-on: https://chromium-review.googlesource.com/705095
Reviewed-by: Andrew Grieve <agrieve@chromium.org>
Reviewed-by: Dirk Pranke <dpranke@chromium.org>
Commit-Queue: John Budorick <jbudorick@chromium.org>
Cr-Commit-Position: refs/heads/master@{#507103}
[modify] https://crrev.com/ab2fa1006465933f0735b392a925746639b422e5/PRESUBMIT.py
[modify] https://crrev.com/ab2fa1006465933f0735b392a925746639b422e5/PRESUBMIT_test.py

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/8ddab7614bf8e067b30a427908a79828ed4b5db2

commit 8ddab7614bf8e067b30a427908a79828ed4b5db2
Author: John Budorick <jbudorick@chromium.org>
Date: Mon Oct 09 16:03:36 2017

[android] Don't write bytecode when running stack.

stack otherwise writes ".../stackc", which our gitignore can't
reasonably ignore.

Bug:  767620 
Change-Id: I838e78488efa6c5c6847930d224ab930a0802438
Reviewed-on: https://chromium-review.googlesource.com/676729
Reviewed-by: Zhiling Huang <hzl@chromium.org>
Commit-Queue: John Budorick <jbudorick@chromium.org>
Cr-Commit-Position: refs/heads/master@{#507386}
[modify] https://crrev.com/8ddab7614bf8e067b30a427908a79828ed4b5db2/build/android/pylib/symbols/stack_symbolizer.py