Fix build with system harfbuzz

build/linux/unbundle/harfbuzz.gyp

 # Copyright 2013 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.
 
 {
   'variables': {
     # Check for presence of harfbuzz-icu library, use it if present.
     'harfbuzz_libraries':
         '<!(python <(DEPTH)/tools/compile_test/compile_test.py '
         '--code "int main() { return 0; }" '
@@ skipping 15 matching lines @@
         ],
       },
       'link_settings': {
         'ldflags': [
           '<!@(pkg-config --libs-only-L --libs-only-other <(harfbuzz_libraries))',
         ],
         'libraries': [
           '<!@(pkg-config --libs-only-l <(harfbuzz_libraries))',
         ],
       },
+      'variables': {
+        'headers_root_path': 'src',
+        'header_filenames': [
+          'hb.h',
+        ],
+      },
+      'includes': [
+        '../../build/shim_headers.gypi',
+      ],
     },
   ],
 }