gpu/gpu_process_host.h is in //content/browser . If it's including stuff in "services/ui/gpu/interfaces/" in a header that's visible to another target (i.e. content_main_runner), I think it needs to be a public dep.

It's a conditional include in content_main_runner.cc

#if !defined(CHROME_MULTIPLE_DLL_BROWSER) && !defined(CHROME_MULTIPLE_DLL_CHILD)
#include "content/browser/gpu/gpu_process_host.h"
#endif

But it's only used to call GpuProcessHost::RegisterGpuMainThreadFactory(..) -- content_main_runner.cc doesn't need all the mojo interfaces. I think there should be a header like src/content/browser/gpu/gpu_main_thread_factory.h

That looks kinda like this I suppose - https://codereview.chromium.org/2675163002/

I don't think content_main_runner has //content/browser as a dep though, does it?

I think it "must", otherwise there'd be link errors?

But for it to depend on the generated header exposed via gpu_process_host.h it would also need to depend on //services/ui/gpu/interfaces. E.g. by //content/browser exposing a public_dep

With the following gn config:

  is_component_build = false
  is_debug = false

It doesn't look like there is a dependency:

  $ gn path out/xx content/app:content_main_runner_both content/browser
  No non-data paths found between these two targets.

So adding to public_deps to content/browser should not affect this.

One alternate* solution would be to always explicitly add services/ui/gpu/interfaces to content_app_deps (because gpu_process_host.h could still be included through some other headers in content_main_runner.cc, so an explicit dep would probably be safest).

*: traditional meaning.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/4091f2f04a14767d816857bd480088c3c62d25d8

commit 4091f2f04a14767d816857bd480088c3c62d25d8
Author: tapted <tapted@chromium.org>
Date: Tue Feb 07 00:47:19 2017

Add gpu_main_thread_factory.h to expose less of content's guts.

gpu_process_host.h exposes a lot of the content layer's guts, including
mojo message files which complicate build depenencies.

Add gpu_main_thread_factory.h to expose the bits that things outside of
content/browser are using. Sepcifically, RegisterGpuMainThreadFactory().

After this, the only files that #include gpu_process_host.h are .cc
files in content/browser or content/public/browser. That is, files built
in a target that already has a dependency on the source of build flakes
coming from //services/ui/gpu/interfaces/.

BUG= 688477 
TBR=avi@chromium.org

Review-Url: https://codereview.chromium.org/2675163002
Cr-Commit-Position: refs/heads/master@{#448472}

[modify] https://crrev.com/4091f2f04a14767d816857bd480088c3c62d25d8/content/app/content_main_runner.cc
[modify] https://crrev.com/4091f2f04a14767d816857bd480088c3c62d25d8/content/browser/BUILD.gn
[add] https://crrev.com/4091f2f04a14767d816857bd480088c3c62d25d8/content/browser/gpu/gpu_main_thread_factory.cc
[add] https://crrev.com/4091f2f04a14767d816857bd480088c3c62d25d8/content/browser/gpu/gpu_main_thread_factory.h
[modify] https://crrev.com/4091f2f04a14767d816857bd480088c3c62d25d8/content/browser/gpu/gpu_process_host.cc
[modify] https://crrev.com/4091f2f04a14767d816857bd480088c3c62d25d8/content/browser/gpu/gpu_process_host.h
[modify] https://crrev.com/4091f2f04a14767d816857bd480088c3c62d25d8/content/public/test/content_test_suite_base.cc

This happened again in:
 - https://build.chromium.org/p/chromium/builders/Win%20x64/builds/8273
 - https://build.chromium.org/p/chromium/builders/Win%20x64/builds/8275

r448472 landed after those (https://build.chromium.org/p/chromium/builders/Win%20x64/builds/8277)

compile failures in 8303,8304 were unrelated. No other failures up to 8315. So I think this is resolved.

re #c6: I think there is a transitive dependency that is missing in gn. adding the necessary direct dependency is forbidden (things should depend on content/public not content). And _not_ having the direct dependency doesn't break since this method call is #if-def'd out on component builds where a link error would likely manifest.