Remove hand-rolled protobufs generation; enable rel paths in protoc.gypi

build/protoc.gypi

Index: build/protoc.gypi
diff --git a/build/protoc.gypi b/build/protoc.gypi
index 555c5be45d29f3e0866eddc6aa996ec6a8a675ad..9a7ec13f0721556abfbeb02986d685aa00061572 100644
--- a/build/protoc.gypi
+++ b/build/protoc.gypi
@@ -43,6 +43,9 @@
     'cc_dir': '<(SHARED_INTERMEDIATE_DIR)/protoc_out/<(proto_out_dir)',
     'py_dir': '<(PRODUCT_DIR)/pyproto/<(proto_out_dir)',
     'proto_in_dir%': '.',
+    # If provided, this must have a trailing slash, otherwise it will be
+    # concatenated with RULE_INPUT_ROOT in 'outputs' and 'action' below.
+    'proto_relpath%': '',
   },
   'rules': [
     {
@@ -52,16 +55,16 @@
         '<(protoc)',
       ],
       'outputs': [
-        '<(py_dir)/<(RULE_INPUT_ROOT)_pb2.py',
-        '<(cc_dir)/<(RULE_INPUT_ROOT).pb.cc',
-        '<(cc_dir)/<(RULE_INPUT_ROOT).pb.h',
+        '<(py_dir)/<(proto_relpath)<(RULE_INPUT_ROOT)_pb2.py',
+        '<(cc_dir)/<(proto_relpath)<(RULE_INPUT_ROOT).pb.cc',
+        '<(cc_dir)/<(proto_relpath)<(RULE_INPUT_ROOT).pb.h',
       ],
       'action': [
         '<(protoc)',
         '--proto_path=<(proto_in_dir)',
         # Naively you'd use <(RULE_INPUT_PATH) here, but protoc requires
         # --proto_path is a strict prefix of the path given as an argument.
-        '<(proto_in_dir)/<(RULE_INPUT_ROOT)<(RULE_INPUT_EXT)',
+        '<(proto_in_dir)/<(proto_relpath)<(RULE_INPUT_ROOT)<(RULE_INPUT_EXT)',
         '--cpp_out=<(cc_dir)',
         '--python_out=<(py_dir)',
         ],