gn2bp: Update --proto_path and --cpp_out arg

--proto_path specify the directory in which to search for imports.
net_quic_proto and metrics_proto have files that import other files.
Get proper --proto_path from the args in the desc.
Also, update --cpp_out to follow --proto_path change.

There are 6 targets which use protoc_wrapper.py in the dependency
from cronet_package_android.
It is confirmed that they could build with this commit.

Test: m cronet_aml_net_isolation_info_proto_gen
      (//net:isolation_info_proto)
Test: m cronet_aml_net_net_nqe_proto_gen
      (//net:net_nqe_proto)
Test: m cronet_aml_net_third_party_quiche_net_quic_test_tools_proto_gen
      (//net/third_party/quiche:net_quic_test_tools_proto)
Test: m cronet_aml_net_cert_root_store_proto_full_gen
      (//net/cert:root_store_proto_full)
Test: m cronet_aml_net_third_party_quiche_net_quic_proto_gen
      (//net/third_party/quiche:net_quic_proto)
Test: m cronet_aml_third_party_metrics_proto_metrics_proto_gen
      (//third_party/metrics_proto:metrics_proto)
Change-Id: Id19e956eb0eb3fb402f8aaa9eb94734b731c74fd
diff --git a/tools/gn2bp/gen_android_bp b/tools/gn2bp/gen_android_bp
index 7d5795a..ffb0741 100755
--- a/tools/gn2bp/gen_android_bp
+++ b/tools/gn2bp/gen_android_bp
@@ -494,13 +494,13 @@
   assert (target.type == 'proto_library')
 
   tools = {'aprotoc'}
-  cpp_out_dir = '$(genDir)/%s/' % tree_path
+  cpp_out_dir = '$(genDir)/%s/%s/' % (tree_path, target.proto_in_dir)
   target_module_name = label_to_module_name(target.name)
 
   # In GN builds the proto path is always relative to the output directory
   # (out/tmp.xxx).
   cmd = ['mkdir -p %s &&' % cpp_out_dir, '$(location aprotoc)']
-  cmd += ['--proto_path=%s' % tree_path]
+  cmd += ['--proto_path=%s/%s' % (tree_path, target.proto_in_dir)]
 
   if buildtools_protobuf_src in target.proto_paths:
     cmd += ['--proto_path=%s' % android_protobuf_src]