fix multithread related crashes in skpdiff

gyp/tools.gyp

 # GYP file to build various tools.
 #
 # To build on Linux:
 #  ./gyp_skia tools.gyp && make tools
 #
 {
   'includes': [
     'apptype_console.gypi',
   ],
   'targets': [
@@ skipping 47 matching lines @@
       'type': 'executable',
       'sources': [
         '../tools/skpdiff/skpdiff_main.cpp',
         '../tools/skpdiff/SkDiffContext.cpp',
         '../tools/skpdiff/SkImageDiffer.cpp',
         '../tools/skpdiff/SkPMetric.cpp',
         '../tools/skpdiff/skpdiff_util.cpp',
         '../tools/flags/SkCommandLineFlags.cpp',
       ],
       'include_dirs': [
-        '../tools/flags'
+        '../tools/flags',
+        '../src/core/', # needed for SkTLList.h
       ],
       'dependencies': [
         'skia_lib.gyp:skia_lib',
       ],
       'cflags': [
         '-O3',
       ],
       'conditions': [
         [ 'skia_os in ["linux", "freebsd", "openbsd", "solaris", "chromeos"]', {
           'link_settings': {
@@ skipping 400 matching lines @@
       },
     ],
   ],
 }
 
 # Local Variables:
 # tab-width:2
 # indent-tabs-mode:nil
 # End:
 # vim: set expandtab tabstop=2 shiftwidth=2: