[inspector_protocol] pass inspector_protocol_dir to inspector_protocol_generate

inspector_protocol.gni

Index: inspector_protocol.gni
diff --git a/inspector_protocol.gni b/inspector_protocol.gni
index 4b161a0981529b5b15cf3a86c2aaa50bb4d40f28..287f84e60b2933ce968db4414a9c7e2aaee52f04 100644
--- a/inspector_protocol.gni
+++ b/inspector_protocol.gni
@@ -23,9 +23,8 @@ template("inspector_protocol_generate") {
   assert(defined(invoker.config_file))
   assert(defined(invoker.out_dir))
   assert(defined(invoker.outputs))
-
-  inspector_protocol_dir =
-      "//third_party/WebKit/Source/platform/inspector_protocol"
+  assert(defined(invoker.inspector_protocol_dir))
+  inspector_protocol_dir = invoker.inspector_protocol_dir
 
   action(target_name) {
     script = "$inspector_protocol_dir/CodeGenerator.py"