Add lots of GN targets

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.
 #
 # Protobuf parameters:
 #
 #   proto_in_dir (optional)
 #       The path to the directory containing the .proto files. If left out, it
@@ skipping 12 matching lines @@
 #       'cc_generator_options' variable with the value:
 #       'dllexport_decl=FOO_EXPORT:' (note trailing colon).
 #
 #       It is likely you also need to #include a file for the above EXPORT
 #       macro to work. See cc_include.
 #
 #   cc_include (optional)
 #       String listing an extra include that should be passed.
 #       Example: cc_include = "foo/bar.h"
 #
+#   deps (optional)
+#       Additional dependencies.
+#
 # Parameters for compiling the generated code:
 #
 #   defines (optional)
 #       Defines to supply to the source set that compiles the generated source
 #       code.
 #
 #   extra_configs (optional)
 #       A list of config labels that will be appended to the configs applying
 #       to the source set.
 #
@@ skipping 75 matching lines @@
       cc_generator_options = invoker.cc_generator_options
     } else {
       cc_generator_options = ""
     }
     args += [
       "--cpp_out", cc_generator_options + rebase_path(cc_dir, root_build_dir),
       "--python_out", rebase_path(py_dir, root_build_dir),
     ]
 
     deps = [ protoc_label ]
+
+    if (defined(invoker.deps)) {
+      deps += invoker.deps
+    }
   }
 
   source_set(target_name) {
     if (defined(invoker.visibility)) {
       visibility = invoker.visibility
     }
 
     sources = get_target_outputs(":$action_name")
 
     if (defined(invoker.defines)) {
       defines = invoker.defines
     }
     if (defined(invoker.extra_configs)) {
       configs += invoker.extra_configs
     }
 
     direct_dependent_configs = [ "//third_party/protobuf:using_proto" ]
 
     deps = [
       ":$action_name",
       "//third_party/protobuf:protobuf_lite",
     ]
 
     # The generated headers reference headers within protobuf_lite, so
     # dependencies must be able to find those headers too.
     forward_dependent_configs_from = [ "//third_party/protobuf:protobuf_lite" ]
   }
 }