Structuring GpuPreferences dependencies

The mojo type GpuPreferences did not depend on the implementation
classes. Since the implementation classes in turn depends on
the mojo bindings, there is a dependency cycle. This patch
describes that in the build system in a way that is accepted
by gn check --check-generated

An example of an error:

ERROR at //out/Default/gen/gpu/ipc/common/gpu_preferences.mojom-forward.h:40:11: Include not allowed.
#include "gpu/config/gpu_preferences.h"
          ^---------------------------
It is not in any dependency of
  //gpu/ipc/common:gpu_preferences_interface
The include file is in the target(s):
  //gpu/config:config_sources
which should somehow be reachable.
___________________


Bug: 938893
Change-Id: I18a9c0c8684ffbbdbe5d47573150434de397061f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1538423
Auto-Submit: Daniel Bratell <bratell@opera.com>
Commit-Queue: Daniel Cheng <dcheng@chromium.org>
Reviewed-by: Antoine Labour <piman@chromium.org>
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Cr-Commit-Position: refs/heads/master@{#644620}
2 files changed