You have to be in tools/perf to run the script.  https://codereview.chromium.org/2519803002/ is out to fix it so you don't have to be in that directory.  Sorry for the confusion. 

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/83e8ca3114f774182150be1bd2e4d85fd0b2c7ec

commit 83e8ca3114f774182150be1bd2e4d85fd0b2c7ec
Author: alancutter <alancutter@chromium.org>
Date: Wed Nov 23 14:53:16 2016

Make generate_perf_json.py work regardless of starting working directory

This patch changes generate_perf_json.py such that you are not required
to cd into tools/perf to be able to run it.

BUG= 667435 

Review-Url: https://codereview.chromium.org/2519803002
Cr-Commit-Position: refs/heads/master@{#434166}

[modify] https://crrev.com/83e8ca3114f774182150be1bd2e4d85fd0b2c7ec/tools/perf/generate_perf_json.py

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/ba78be88a98b57c9e4195c59a26156a4c3cf4765

commit ba78be88a98b57c9e4195c59a26156a4c3cf4765
Author: alancutter <alancutter@chromium.org>
Date: Mon Dec 05 00:02:04 2016

Remove cwd logic from generate_perf_json.py

This patch refactors generate_perf_json.py to avoid using cwd logic.
File paths are now relative to src which is derived relative to the
script location.

BUG= 667435 

Review-Url: https://codereview.chromium.org/2542073003
Cr-Commit-Position: refs/heads/master@{#436208}

[modify] https://crrev.com/ba78be88a98b57c9e4195c59a26156a4c3cf4765/tools/perf/generate_perf_json.py

Emily - when you're back, can we close this? I don't know if your CLs fixed this or not as I'm not sure how to verify.

(Just tested it and it works fine now.)