Add proto_in_dir to cc_grpc_library forwarding

This change adds the ability to forward proto_in_dir to support
downstream use of nested directories for grpc protobufs.

Bug: 1129637
Change-Id: I0221d7b1a28aa578c8f3f33cd93b6d07879c54f2
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2416568
Commit-Queue: Brandon Tolsch <btolsch@chromium.org>
Reviewed-by: Luke Halliwell (slow) <halliwell@chromium.org>
Reviewed-by: Nico Weber <thakis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#808114}

third_party/.gitignore

@@ -91,7 +91,7 @@
 /google_benchmark/src
 /google_toolbox_for_mac/src
 /googlemac
-/grpc
+/grpc/src
 /gvr-android-sdk/common_library.aar
 /gvr-android-sdk/test-libraries/controller_test_api.aar
 /gvr-android-sdk/libgvr_shim_static_*.a

third_party/grpc/grpc_library.gni

@@ -22,6 +22,7 @@ template("cc_grpc_library") {
                              "sources",
                              "use_protobuf_full",
                              "import_dirs",
+                             "proto_in_dir",
                            ])
     remove_configs = [ "//build/config/compiler:chromium_code" ]
     extra_configs = [