Occasionally, local_test_server_posix fails to start like this:

[32633:775:1226/024159.485462:191388426679899:ERROR:local_test_server_posix.cc(79)] poll() timed out; bytes_read=0
[32633:775:1226/024159.485501:191388426712695:ERROR:local_test_server_posix.cc(167)] Could not read server_data_len
../../chrome/browser/safe_browsing/download_protection/two_phase_uploader_unittest.cc:120: Failure
Value of: test_server.Start()
  Actual: false
Expected: true
Stack trace:
0   unit_tests                          0x000000010ebfbb5b unit_tests + 30444379
1   unit_tests                          0x000000010ebfb479 unit_tests + 30442617
2   unit_tests                          0x000000010e745406 unit_tests + 25502726

This flakes ~every test that needs it.

Sample failed builds:

https://uberchromegw.corp.google.com/i/official.desktop/builders/mac64/builds/3801
https://uberchromegw.corp.google.com/i/official.desktop/builders/mac64/builds/3766