[GRC] GRC service plumbing in Blink.

services/resource_coordinator/public/interfaces/BUILD.gn

 # Copyright 2017 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import("//mojo/public/tools/bindings/mojom.gni")
 
 mojom("interfaces_internal") {
   visibility = [ "//services/resource_coordinator/public/cpp:*" ]
+  visibility_blink = [ "//third_party/WebKit/Source/platform/*" ]

[oystein (OOO til 10th of July), 2017/06/02 15:32:36]

I don't think this is right. The reason for wrapping the Mojo interfaces
together with the public/cpp stuff is so the whole service can be built as a
component, due to the use of statics in the clientlib.

We're depending on
//services/resource_coordinator/public/cpp:resource_coordinator_cpp anyway,
can't that component internally depend on
//services/resource_coordinator/public/interfaces:interfaces_internal_blink ?

+rockot who knows this service component build magic :P.

[Ken Rockot(use gerrit already), 2017/06/02 17:01:23]

Blink and non-blink variant target outputs are totally separate. So your
export_* settings below only apply to the non-blink version. If you depend on
interfaces_internal_blink from your cpp component, it wouldn't export the blink
mojom symbols.

Now you could do that and add export_class_attribute_blink etc with the same
values. Then you would of course also get rid of the interfaces_internal_blink
dependency this CL is adding in Blink.

Another option would be to stop using this component magic and use the other
component magic, which makes your interfaces targets (e.g. "interfaces" and
"interfaces_blink") components themselves. i.e.

 mojom_component("interfaces") {
  sources = [ ... ]
  output_prefix = "resource_coordinator_interfaces"
  macro_prefix = "RESOURCE_COORDINATOR_INTERFACES"
 }

The trade-off (isn't there always a trade-off) with this new approach is that
you have to split your client library into two parts to avoid circular deps:
 - a component for any types that are typemapped from mojom. This can't depend
on the mojom itself obviously (the mojom depends on it via typemap)
 - a component for everything else, which depends on both the first component
and the mojom target(s) as needed

[lpy, 2017/06/02 20:23:52]

Done.

 
   sources = [
     "coordination_unit.mojom",
     "coordination_unit_provider.mojom",
     "events.mojom",
     "memory_instrumentation/constants.mojom",
     "memory_instrumentation/memory_instrumentation.mojom",
     "service_constants.mojom",
     "tracing/tracing.mojom",
   ]
 
   public_deps = [
     "//mojo/common:common_custom_types",
   ]
 
   component_output_prefix = "resource_coordinator_public_interfaces_internal"
   export_class_attribute = "SERVICES_RESOURCE_COORDINATOR_PUBLIC_CPP_EXPORT"
   export_define = "SERVICES_RESOURCE_COORDINATOR_PUBLIC_CPP_IMPLEMENTATION=1"
   export_header =
       "services/resource_coordinator/public/cpp/resource_coordinator_export.h"
 
   # TODO(crbug.com/714018): Convert the implementation to use OnceCallback.
   use_once_callback = false
 }