Make more services' public interfaces flexible wrt location in repo.

mojo/services/gpu/public/interfaces/gpu.mojom

Index: mojo/services/gpu/public/interfaces/gpu.mojom
diff --git a/mojo/services/gpu/public/interfaces/gpu.mojom b/mojo/services/gpu/public/interfaces/gpu.mojom
index 4e0ef5137350c469590ffd12fb927ad75bbf6bcc..05823fc81f8a7103241e30ad8d8b765723172114 100644
--- a/mojo/services/gpu/public/interfaces/gpu.mojom
+++ b/mojo/services/gpu/public/interfaces/gpu.mojom
@@ -4,9 +4,9 @@
 
 module mojo;
 
-import "mojo/services/geometry/public/interfaces/geometry.mojom";
-import "mojo/services/gpu/public/interfaces/command_buffer.mojom";
-import "mojo/services/gpu/public/interfaces/viewport_parameter_listener.mojom";
+import "../../../geometry/public/interfaces/geometry.mojom";

[jamesr, 2015/01/08 19:07:46]

this is really weird.  It sorta makes sense for some cases like C++ where we're
pretty constrained by existing code and setups, but for mojom I think we can try
to do better

what about having mojom targets declare their paths relative to some root (i.e.
mojo/services/gpu/public/interfaces/ can have all of its paths be relative to
//mojo/services) and export that in the public_configs of the mojom template?
Then if you use public_deps correctly (which you should anyway) then you get
include paths from things you declare dependencies on and can write imports like
this:

import "geometry/public/interfaces/geometry.mojom";
import "gpu/public/interfaces/gpu.mojom";

etc


in practice with the //mojo/services/XXX/public family this means they'll all
add //mojo/services to the mojom include path, but if these move then they'll
still work

[blundell, 2015/01/09 10:08:07]

If I understand what you're suggesting correctly, the mojom template would have
to be able to loop through all the "import_dirs" that are added to a given
target from its deps adding each one as a "-I" arg to the generator_script. I
don't think this is possible: AFAIK a target cannot see configs that are added
to it by its deps via public_configs (cf. "gn help public_configs"). (There is
also a more minor problem that a config can only set a restricted set of
variables, so these "import_dirs" would have to be specified as include_dirs,
which seems icky to me as it is conflating include paths at the mojom level and
the C++ level).

+import "command_buffer.mojom";
+import "viewport_parameter_listener.mojom";
 
 interface Gpu {
   CreateOnscreenGLES2Context(uint64 native_viewport_id,