Support more configurability in GN toolchains

tools/gn/BUILD.gn

Index: tools/gn/BUILD.gn
diff --git a/tools/gn/BUILD.gn b/tools/gn/BUILD.gn
index 7832727de68755e45bba0af14d7120fa4bff285d..e3724ad9425da6aa4f75f8e138f653ce5fbad05e 100644
--- a/tools/gn/BUILD.gn
+++ b/tools/gn/BUILD.gn
@@ -93,8 +93,8 @@ static_library("gn_lib") {
     "ninja_copy_target_writer.h",
     "ninja_group_target_writer.cc",
     "ninja_group_target_writer.h",
-    "ninja_helper.cc",
-    "ninja_helper.h",
+    "ninja_utils.cc",
+    "ninja_utils.h",
     "ninja_target_writer.cc",
     "ninja_target_writer.h",
     "ninja_toolchain_writer.cc",
@@ -103,6 +103,7 @@ static_library("gn_lib") {
     "ninja_writer.h",
     "operators.cc",
     "operators.h",
+    "output_file.cc",
     "output_file.h",
     "parse_tree.cc",
     "parse_tree.h",
@@ -126,6 +127,8 @@ static_library("gn_lib") {
     "source_dir.h",
     "source_file.cc",
     "source_file.h",
+    "source_file_type.cc",
+    "source_file_type.h",
     "standard_out.cc",
     "standard_out.h",
     "string_utils.cc",
@@ -147,6 +150,8 @@ static_library("gn_lib") {
     "token.cc",
     "token.h",
     "tokenizer.cc",
+    "tool.cc",
+    "tool.h",
     "tokenizer.h",
     "toolchain.cc",
     "toolchain.h",
@@ -204,8 +209,8 @@ test("gn_unittests") {
     "ninja_action_target_writer_unittest.cc",
     "ninja_binary_target_writer_unittest.cc",
     "ninja_copy_target_writer_unittest.cc",
-    "ninja_helper_unittest.cc",
     "ninja_target_writer_unittest.cc",
+    "ninja_toolchain_writer_unittest.cc",
     "operators_unittest.cc",
     "parse_tree_unittest.cc",
     "parser_unittest.cc",