Thank you for tracking this!

Thanks for spotting this csharrison@!

I found where the problem is. For history navigations, the old path has two cases for back/forward navigation load flags: https://cs.chromium.org/chromium/src/third_party/WebKit/Source/core/loader/FrameFetchContext.cpp?rcl=e7aca0670b59b9062005a9b5a96cfb2d29743682&l=250. However, the PlzNavigate is missing an else statement: https://cs.chromium.org/chromium/src/content/browser/frame_host/navigation_request.cc?rcl=e7aca0670b59b9062005a9b5a96cfb2d29743682&l=87.

I have a CL with a fix and a test for this.

Ah, the CL is https://codereview.chromium.org/2780353005/ :).

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/7ee0fa238b36d1f1a12a240f2caf025559727ec4

commit 7ee0fa238b36d1f1a12a240f2caf025559727ec4
Author: nasko <nasko@chromium.org>
Date: Fri Mar 31 21:54:44 2017

Fix history navigations in PlzNavigate to use the proper load flags.

There is a difference in flags between the regular navigation path and
PlzNavigate. This CL fixes the new path to have the same logic as the
existing one.

BUG= 707282 
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:linux_site_isolation

Review-Url: https://codereview.chromium.org/2780353005
Cr-Commit-Position: refs/heads/master@{#461240}

[modify] https://crrev.com/7ee0fa238b36d1f1a12a240f2caf025559727ec4/content/browser/frame_host/navigation_controller_impl_browsertest.cc
[modify] https://crrev.com/7ee0fa238b36d1f1a12a240f2caf025559727ec4/content/browser/frame_host/navigation_request.cc
[add] https://crrev.com/7ee0fa238b36d1f1a12a240f2caf025559727ec4/content/test/data/navigation_controller/page_with_no_cache_header.html
[add] https://crrev.com/7ee0fa238b36d1f1a12a240f2caf025559727ec4/content/test/data/navigation_controller/page_with_no_cache_header.html.mock-http-headers

I'll resolve this one as fixed, since it has an explicit test for it.

Apologies, applied the wrong component in bulk.