Use list_dart_files.py instead of list_files.py in GN build.

pkg/BUILD.gn

Index: pkg/BUILD.gn
diff --git a/pkg/BUILD.gn b/pkg/BUILD.gn
index d8efcf8aa7401302c7bec8d031e7ebce3cd1899c..8dc602f35b585c5edcaf6672b513c7c72318ba75 100644
--- a/pkg/BUILD.gn
+++ b/pkg/BUILD.gn
@@ -5,7 +5,6 @@
 import("../utils/create_timestamp.gni")
 
 template("make_third_party_pkg_files_stamp") {
-  assert(defined(invoker.pattern), "Must define the file pattern")
   assert(defined(invoker.id), "Must define the stamp file id")
   path = rebase_path("../third_party/pkg")
   if (defined(invoker.path)) {
@@ -13,7 +12,9 @@ template("make_third_party_pkg_files_stamp") {
   }
   id = invoker.id
   create_timestamp_file(target_name) {
-    pattern = invoker.pattern
+    if (defined(invoker.pattern)) {
+      pattern = invoker.pattern
+    }
     path = path
     new_base = "//"
     output = "$target_gen_dir/third_party_pkg_files_$id.stamp"
@@ -21,23 +22,22 @@ template("make_third_party_pkg_files_stamp") {
 }
 
 make_third_party_pkg_files_stamp("make_third_party_pkg_files_0_stamp") {
-  pattern = "^(?!.*/test/).*(?<!_test)[.]dart\$"
   path = rebase_path(".")
   id = "0"
 }
 
 make_third_party_pkg_files_stamp("make_third_party_pkg_files_1_stamp") {
-  pattern = "^(?!.*_test\.dart).*[a-k]\.dart\$"
+  pattern = "[a-k].*"
   id = "1"
 }
 
 make_third_party_pkg_files_stamp("make_third_party_pkg_files_2_stamp") {
-  pattern = "^(?!.*_test\.dart).*[l-r]\.dart\$"
+  pattern = "[l-r].*"
   id = "2"
 }
 
 make_third_party_pkg_files_stamp("make_third_party_pkg_files_3_stamp") {
-  pattern = "^(?!.*_test\.dart).*[^a-r]\.dart\$"
+  pattern = "[s-z].*"
   id = "3"
 }
 
@@ -54,11 +54,10 @@ action("pkg_files_stamp") {
   stamp2_outputs = get_target_outputs(":make_third_party_pkg_files_2_stamp")
   stamp3_outputs = get_target_outputs(":make_third_party_pkg_files_3_stamp")
 
-  inputs = ["../tools/list_files.py"] +
-      stamp0_outputs +
-      stamp1_outputs +
-      stamp2_outputs +
-      stamp3_outputs
+  inputs = stamp0_outputs +
+           stamp1_outputs +
+           stamp2_outputs +
+           stamp3_outputs
 
   outputs = [
     "$root_gen_dir/pkg_files.stamp"