More work on content/browser GN build.

third_party/protobuf/proto_library.gni

 # Copyright 2014 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 # Compile a protocol buffer.
 #
-# The 'proto_in_dir' variable must be the relative path to the
-# directory containing the .proto files. If left out, it defaults to '.'.
+# The 'proto_in_dir' variable is the path to the directory containing the
+# .proto files. If left out, it defaults to '.'.
 #
 # The 'proto_out_dir' variable specifies the path suffix that output files are
 # generated under.  Targets that gyp-depend on my_proto_lib will be able to
 # include the resulting proto headers with an include like:
 #   #include "dir/for/my_proto_lib/foo.pb.h"
 # If undefined, this defaults to matching the input directory.
 #
 # If you need to add an EXPORT macro to a protobuf's C++ header, set the
 # 'cc_generator_options' variable with the value: 'dllexport_decl=FOO_EXPORT:'
 # e.g. 'dllexport_decl=BASE_EXPORT:'
@@ skipping 97 matching lines @@
     sources = get_target_outputs(":$action_name")
 
     direct_dependent_configs = [ "//third_party/protobuf:using_proto" ]
 
     deps = [
       ":$action_name",
       "//third_party/protobuf:protobuf_lite",
     ]
   }
 }