Make blink's mojo geometry types depend publicly on the struct_traits

Generated code that use the mojo geometry types will end up
including geometry_struct_traits.h and for that to be allowed
by the build system, the dependency in the typemap needs to
be public.

An example (of about 100) error:

ERROR at //out/Default/gen/device/vr/public/mojom/isolated_xr_service.mojom-blink-test-utils.cc:33:11: Can't include this header from here.
          ^----------------------------------------------------------------
The target:
  //device/vr/public/mojom:mojom_blink
is including a file from the target:
  //third_party/blink/renderer/platform/mojo:geometry_struct_traits

It's usually best to depend directly on the destination target.
In some cases, the destination target is considered a subcomponent
of an intermediate target. In this case, the intermediate target
should depend publicly on the destination to forward the ability
to include headers.

Dependency chain (there may also be others):
  //device/vr/public/mojom:mojom_blink -->
  //ui/gfx/geometry/mojo:mojo_blink --[private]-->
  //third_party/blink/renderer/platform/mojo:geometry_struct_traits


Bug: 938893
Change-Id: I2114034805ee2e55a8c98e98c22fe8233ac9fd61
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1538418
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Commit-Queue: Daniel Bratell <bratell@opera.com>
Cr-Commit-Position: refs/heads/master@{#644225}
diff --git a/third_party/blink/renderer/platform/mojo/geometry.typemap b/third_party/blink/renderer/platform/mojo/geometry.typemap
index 5a7f96c..5675e71e 100644
--- a/third_party/blink/renderer/platform/mojo/geometry.typemap
+++ b/third_party/blink/renderer/platform/mojo/geometry.typemap
@@ -18,6 +18,9 @@
 # Note: consumers of this typemap must themselves depend on platform.
 deps = [
   "//mojo/public/cpp/bindings",
+]
+
+public_deps = [
   "//third_party/blink/renderer/platform/mojo:geometry_struct_traits",
 ]