Optionally compute grit inputs precisely.

content/browser/devtools/BUILD.gn

 # 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.
 
 import("//tools/grit/grit_rule.gni")
 
 group("resources") {
   public_deps = [
     ":devtools_resources",
   ]
 }
 
 grit("devtools_resources") {
   source = "$root_gen_dir/devtools/devtools_resources.grd"
+  source_is_generated = true
 
   # TOOD(brettw) remove this so the output file goes into the target_gen_dir,
   # but keep this for not for GYP compat.
   output_dir = "$root_gen_dir/blink"
   outputs = [
     "grit/devtools_resources.h",
     "devtools_resources.pak",
     "grit/devtools_resources_map.cc",
     "grit/devtools_resources_map.h",
   ]
@@ skipping 21 matching lines @@
   ]
 
   outputs = [
     "$target_gen_dir/protocol/devtools_protocol_dispatcher.cc",
     "$target_gen_dir/protocol/devtools_protocol_dispatcher.h",
   ]
 
   args =
       rebase_path(inputs, root_build_dir) + rebase_path(outputs, root_build_dir)
 }