Optionally compute grit inputs precisely.

content/browser/tracing/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")
 
 # generate_about_tracing puts its files in this directory
 tracing_gen_dir = "$root_gen_dir/content/browser/tracing"
 
 # The script just writes filename with no dirs to the .grd, so we always need
@@ skipping 18 matching lines @@
            rebase_path(tracing_grd, root_build_dir),
          ]
 
   deps = [
     "//third_party/catapult/tracing:generate_about_tracing",
   ]
 }
 
 grit("resources") {
   source = tracing_grd
+  source_is_generated = true
+
   outputs = [
     "grit/tracing_resources.h",
     "tracing_resources.pak",
   ]
 
   # resource_ids has an entry for our .grd file that looks like:
   # "<(SHARED_INTERMEDIATE_DIR)/content/browser/tracing/tracing_resources.grd"
   # and what we pass here should make that resolve to our .grd file.
   defines =
       [ "SHARED_INTERMEDIATE_DIR=" + rebase_path(root_gen_dir, root_build_dir) ]
 
   deps = [
     ":generate_tracing_grd",
   ]
 }