Add basic stacktrace handler using libunwind.

gyp/gm.gyp

 # GYP file to build the "gm" (golden master) executable.
 {
   'includes': [
     'apptype_console.gypi',
   ],
   'targets': [
     {
       'target_name': 'gm_expectations',
       'type': 'static_library',
       'include_dirs' : [
         '../src/utils/',
       ],
       'sources': [
         '../gm/gm_expectations.h',
         '../gm/gm_expectations.cpp',
         '../tools/sk_tool_utils.cpp',
       ],
       'dependencies': [
+        'crash_handler.gyp:CrashHandler',
+        'jsoncpp.gyp:jsoncpp',
         'skia_lib.gyp:skia_lib',
-        'jsoncpp.gyp:jsoncpp',
       ],
       'direct_dependent_settings': {
         'include_dirs': [
           '../gm/',
         ],
       },
     },
     {
       'target_name': 'gm',
       'type': 'executable',
@@ skipping 77 matching lines @@
             '../src/gpu',
           ],
           'dependencies': [
             'gputest.gyp:skgputest',
           ],
         }],
       ],
     },
   ],
 }