Seen this here:
https://build.chromium.org/p/tryserver.chromium.linux/builders/linux_chromium_rel_ng/builds/464879

Also here:
https://build.chromium.org/p/tryserver.chromium.linux/builders/linux_chromium_rel_ng/builds/464902

20515 2017-05-25 21:10:15.704 E: Failed to fetch 96883c91301e5cd5446c4b9e4aaddecf71b96f5b: Incorrect file size: expected 845812264, got 11947331
20515 2017-05-25 21:10:32.314 E: Failed to fetch 96883c91301e5cd5446c4b9e4aaddecf71b96f5b: Incorrect file size: expected 845812264, got 11947331
20515 2017-05-25 21:10:49.063 E: Failed to fetch 96883c91301e5cd5446c4b9e4aaddecf71b96f5b: Incorrect file size: expected 845812264, got 41913847
20515 2017-05-25 21:11:04.675 E: Failed to fetch 96883c91301e5cd5446c4b9e4aaddecf71b96f5b: Incorrect file size: expected 845812264, got 41913847
20515 2017-05-25 21:11:21.122 E: Failed to fetch 96883c91301e5cd5446c4b9e4aaddecf71b96f5b: Incorrect file size: expected 845812264, got 391239897
20515 2017-05-25 21:11:38.847 E: Failed to fetch 96883c91301e5cd5446c4b9e4aaddecf71b96f5b: Incorrect file size: expected 845812264, got 465293801
20515 2017-05-25 21:11:39.207 E: internal failure: Incorrect file size: expected 845812264, got 465293801
Traceback (most recent call last):
  File "/b/s/swarming_bot.1.zip/client/run_isolated.py", line 483, in map_and_run
    use_symlinks=use_symlinks)
  File "/b/s/swarming_bot.1.zip/client/run_isolated.py", line 314, in fetch_and_map
    use_symlinks=use_symlinks)
  File "/b/s/swarming_bot.1.zip/client/isolateserver.py", line 1654, in fetch_isolated
    digest = fetch_queue.wait(remaining)
  File "/b/s/swarming_bot.1.zip/client/isolateserver.py", line 810, in wait
    digest = self._channel.pull()
  File "/b/s/swarming_bot.1.zip/utils/threading_utils.py", line 377, in _task_executer
    result = func(*args, **kwargs)
  File "/b/s/swarming_bot.1.zip/client/isolateserver.py", line 663, in fetch
    sink(verifier.run())
  File "/b/s/swarming_bot.1.zip/client/isolateserver.py", line 1237, in write
    size = file_write(path, content)
  File "/b/s/swarming_bot.1.zip/client/isolateserver.py", line 135, in file_write
    for d in content_generator:
  File "/b/s/swarming_bot.1.zip/client/isolateserver.py", line 870, in run
    self._inspect_chunk(stored, is_last=True)
  File "/b/s/swarming_bot.1.zip/client/isolateserver.py", line 884, in _inspect_chunk
    self.expected_size, self.current_size))
IOError: Incorrect file size: expected 845812264, got 465293801
Sending the crash report ... done.
Report URL: https://isolateserver.appspot.com/restricted/ereporter2/errors/6163234490941440
Incorrect file size: expected 845812264, got 465293801

maruel@, could you please triage?