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}

gpu/config/BUILD.gn

@@ -161,6 +161,11 @@ jumbo_source_set("config_sources") {
     "//ui/gl/init",
   ]
 
+  # GpuPreferences is using its own mojo bindings which creates a
+  # cycle between this target and gpu_preferences_interface.
+  allow_circular_includes_from =
+      [ "//gpu/ipc/common:gpu_preferences_interface" ]
+
   # Prefer mesa GL headers to system headers, which cause problems on Win.
   include_dirs = [ "//third_party/mesa_headers" ]
 

gpu/ipc/common/gpu_preferences.typemap

@@ -8,6 +8,15 @@ traits_headers = [ "//gpu/ipc/common/gpu_preferences_struct_traits.h" ]
 public_deps = [
   "//media:media_buildflags",
 ]
+deps = [
+  # We depend on gpu_preferences but since it also depends on its own
+  # mojo bindings, that is handled with an |allowed_circular_includes|
+  # in //gpu/config:gpu_preferences.
+  # "//gpu/config:gpu_preferences",
+]
+sources = [
+  "//gpu/ipc/common/gpu_preferences_struct_traits.h",
+]
 type_mappings = [
   "gpu.mojom.GpuPreferences=gpu::GpuPreferences",
   "gpu.mojom.VpxDecodeVendors=gpu::GpuPreferences::VpxDecodeVendors",