My preference is to separate transport security tests into two categories (1) general functionality tests (2) tests that asserts on correctness of the real preload list. 

For (1), those tests shouldn't rely on the real preload list, but on transport_security_state_static_unittest0.json.
For (2), we disable these tests if INCLUDE_TRANSPORT_SECURITY_STATE_PRELOAD_LIST is undefined.

That sounds fine.

Would you have any time to do that? :-)

No. Unfortunately, I am swamped with things that I need to do. 
I am not the best person to do this though -- my understanding of Transport Security concepts is really minimal :)

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/b1383dad418304962de75e402ea25d645d02092c

commit b1383dad418304962de75e402ea25d645d02092c
Author: Martijn Croonen <martijn@martijnc.be>
Date: Wed Oct 11 11:56:35 2017

Split up transport security state related tests.

All transport security state tests currently depend on the real preload
list. This has caused issues when the preload list is updated. This CL
splits up the tests in two categories:

  1: tests that test functionality related to the static transport
     security state implementation.
  2: tests that assert the correctness of the real preload list.

The tests that fall under (1) no longer depend on entries in the real
preload list but use a test-only preload list. The entries in (2) use
the real preload list but are disabled when the preload list is not
used.

Bug:  767108 
Change-Id: I71ad58670d0e2366d76602b5a6d799e3c48269a4
Reviewed-on: https://chromium-review.googlesource.com/706786
Reviewed-by: Lucas Garron <lgarron@chromium.org>
Reviewed-by: Helen Li <xunjieli@chromium.org>
Commit-Queue: Martijn Croonen <martijnc@chromium.org>
Cr-Commit-Position: refs/heads/master@{#507954}
[modify] https://crrev.com/b1383dad418304962de75e402ea25d645d02092c/net/BUILD.gn
[modify] https://crrev.com/b1383dad418304962de75e402ea25d645d02092c/net/http/BUILD.gn
[modify] https://crrev.com/b1383dad418304962de75e402ea25d645d02092c/net/http/http_security_headers_unittest.cc
[delete] https://crrev.com/be40400e2f2c19fea7aed40e64d470f0dd5814af/net/http/transport_security_state_static_unittest0.json
[add] https://crrev.com/b1383dad418304962de75e402ea25d645d02092c/net/http/transport_security_state_static_unittest_default.json
[add] https://crrev.com/b1383dad418304962de75e402ea25d645d02092c/net/http/transport_security_state_static_unittest_default.pins
[modify] https://crrev.com/b1383dad418304962de75e402ea25d645d02092c/net/http/transport_security_state_unittest.cc
[modify] https://crrev.com/b1383dad418304962de75e402ea25d645d02092c/net/tools/transport_security_state_generator/README.md
[modify] https://crrev.com/b1383dad418304962de75e402ea25d645d02092c/net/url_request/url_request_unittest.cc