Support more configurability in GN toolchains

tools/gn/source_file_type.h

Index: tools/gn/source_file_type.h
diff --git a/tools/gn/source_file_type.h b/tools/gn/source_file_type.h
new file mode 100644
index 0000000000000000000000000000000000000000..f8d9a098690b73bfa46bc8d285f58b6527031585
--- /dev/null
+++ b/tools/gn/source_file_type.h
@@ -0,0 +1,25 @@
+// 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.
+
+#ifndef TOOLS_GN_SOURCE_FILE_TYPE_H_
+#define TOOLS_GN_SOURCE_FILE_TYPE_H_
+
+class SourceFile;
+
+enum SourceFileType {
+  SOURCE_UNKNOWN,
+  SOURCE_ASM,
+  SOURCE_C,
+  SOURCE_CC,
+  SOURCE_H,
+  SOURCE_M,
+  SOURCE_MM,
+  SOURCE_S,
+  SOURCE_RC,
+  SOURCE_O,  // Object files can be inputs, too. Also counts .obj.
+};
+
+SourceFileType GetSourceFileType(const SourceFile& file);
+
+#endif  // TOOLS_GN_SOURCE_FILE_TYPE_H_