A snippet of the std output shows 13 files being deleted from temp:

C:\b\depot_tools\win_tools-2_7_6_bin\python\bin\python.exe C:\b\rr\tmpjvvrby\rw\checkout\scripts\slave\runisolatedtest.py --test_name sizes --builder_name "Google Chrome Win" --checkout_dir C:\b\c\b\win_chrome C:\b\c\b\win_chrome\src\infra\scripts\legacy\scripts\slave\chromium\sizes.py -- C:\b\depot_tools\win_tools-2_7_6_bin\python\bin\python.exe C:\b\c\b\win_chrome\src\infra\scripts\legacy\scripts\slave\chromium\sizes.py --target Release --platform win
C:\b\depot_tools\win_tools-2_7_6_bin\python\bin\python.exe C:\b\c\b\win_chrome\src\infra\scripts\legacy\scripts\slave\chromium\sizes.py --target Release --platform win
RESULT chrome.dll: chrome.dll= 44724736 bytes
RESULT chrome.dll.pdb: chrome.dll.pdb= 1093939200 bytes
RESULT chrome.exe: chrome.exe= 1455104 bytes
RESULT chrome_child.dll: chrome_child.dll= 66278400 bytes
RESULT chrome_child.dll.pdb: chrome_child.dll.pdb= 1257861120 bytes
RESULT chrome_elf.dll: chrome_elf.dll= 463360 bytes
RESULT chrome_watcher.dll: chrome_watcher.dll= 528384 bytes
RESULT libEGL.dll: libEGL.dll= 78848 bytes
RESULT libGLESv2.dll: libGLESv2.dll= 3893248 bytes
RESULT mini_installer.exe: mini_installer.exe= 49576960 bytes
RESULT resources.pak: resources.pak= 12893767 bytes
RESULT setup.exe: setup.exe= 1643008 bytes
RESULT swiftshader\libEGL.dll: swiftshader\libEGL.dll= 102912 bytes
RESULT swiftshader\libGLESv2.dll: swiftshader\libGLESv2.dll= 2233344 bytes
RESULT WidevineCdm\_platform_specific\win_x86\widevinecdm.dll: WidevineCdm\_platform_specific\win_x86\widevinecdm.dll= 6179672 bytes
44724736
<Thread(Thread-1, started 7380)> ProcessRead: proc.stdout finished.
<Thread(Thread-1, started 7380)> ProcessRead: cleaning up.
<Thread(Thread-2, started daemon 5536)> TimedFlush: Finished
<Thread(Thread-1, started 7380)> ProcessRead: finished.
exit code (as seen by runtest.py): 1
Sending result 2 of 2 to dashboard.
Confused: 13 files were deleted from c:\users\chrome~1\appdata\local\temp during the test run
step returned non-zero exit code: 1

The regression range given is https://test-results.appspot.com/revision_range?start=551888&end=551901, but I don't see anything that I think is related. Tagging Infra-Troopers to see if this may be an infra issue.

Seems that it started to fail here:
https://ci.chromium.org/buildbot/chromium.chrome/Google%20Chrome%20Win/29314

I wonder if it could be related to changes made recently by rsesek@
https://chromium-review.googlesource.com/c/chromium/src/+/1017061
https://chromium-review.googlesource.com/c/chromium/tools/build/+/1017563

 Issue 834786  has been merged into this issue.

This is what the code looks like now:

```
def main_win(...):
  ...
  result = 0

  for f in files:
    p = os.path.join(target_dir, f)
    if os.path.isfile(p):
      this_result = get_size(p) # Gets the file size of p in bytes
      if result == 0:
        result = this_result
      results_collector.add_result(f, f, this_result, 'bytes')

  return result
```

And the caller in main treats that as an exit code and returns it, so it's going to be non-zero.

Thanks for catching that Reid! Manual-merge fail.

https://chromium-review.googlesource.com/#/c/chromium/src/+/1019980

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/70c56b8ff35427244ef484c2b176421a80d76da9

commit 70c56b8ff35427244ef484c2b176421a80d76da9
Author: Robert Sesek <rsesek@chromium.org>
Date: Thu Apr 19 19:58:34 2018

Fix a bug in sizes.py on Windows where main_win() was returning non-zero.

This was caused by an erroneous manual merge in
15bbc3bf959efe5264443bea08f99a77b44f7921.

Bug:  783855 ,  834604 
Change-Id: I1f821b5c86d7c11478f4430f68bce58238c1d9bc
Reviewed-on: https://chromium-review.googlesource.com/1019980
Reviewed-by: Dirk Pranke <dpranke@chromium.org>
Commit-Queue: Robert Sesek <rsesek@chromium.org>
Cr-Commit-Position: refs/heads/master@{#552132}
[modify] https://crrev.com/70c56b8ff35427244ef484c2b176421a80d76da9/infra/scripts/legacy/scripts/slave/chromium/sizes.py

https://ci.chromium.org/buildbot/chromium.chrome/Google%20Chrome%20Win/29352