GN: only include headers in echo_headers.py

gn/echo_headers.py

 #!/usr/bin/env python
 #
 # Copyright 2016 Google Inc.
 #
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import sys
 import os
 import os.path
 
 blacklist = [
   'GrGLConfig_chrome.h',
   'SkFontMgr_fontconfig.h',
 ]
 
 headers = []
 for d in sys.argv[2:]:
   headers.extend([f for f in os.listdir(d)
-                  if os.path.isfile(os.path.join(d,f))])
+                  if os.path.isfile(os.path.join(d,f)) and f.endswith('.h')])
 with open(sys.argv[1], "w") as f:
   f.write('// skia.h generated by GN.\n')
   f.write('#ifndef skia_h_DEFINED\n')
   f.write('#define skia_h_DEFINED\n')
   for h in headers:
     if h not in blacklist:
       f.write('#include "' + h + '"\n')
   f.write('#endif//skia_h_DEFINED\n')