DM: add --serialize

gyp/dm.gyp

 # GYP for "dm" (Diamond Master, a.k.a Dungeon master, a.k.a GM 2).
 # vim: set expandtab tabstop=4 shiftwidth=4
 {
     'includes': [ 'apptype_console.gypi' ],
 
     'targets': [{
         'target_name': 'dm',
         'type': 'executable',
         'include_dirs': [
             '../dm',
             '../gm',
             '../src/core',
             '../src/effects',
             '../src/utils',
             '../src/utils/debugger',
         ],
         'includes': [ 'gmslides.gypi' ],
         'sources': [
             '../dm/DM.cpp',
             '../dm/DMComparisonTask.cpp',
             '../dm/DMCpuTask.cpp',
             '../dm/DMGpuTask.cpp',
             '../dm/DMReplayTask.cpp',
             '../dm/DMReporter.cpp',
+            '../dm/DMSerializeTask.cpp',
             '../dm/DMTask.cpp',
             '../dm/DMTaskRunner.cpp',
             '../dm/DMUtil.cpp',
             '../dm/DMWriteTask.cpp',
             '../gm/gm.cpp',
             '../gm/gm_expectations.cpp',
 
             # TODO: split these out as a library in src/utils/debugger.
             '../src/utils/debugger/SkDebugCanvas.cpp',
             '../src/utils/debugger/SkDrawCommand.cpp',
             '../src/utils/debugger/SkObjectParser.cpp',
         ],
         'dependencies': [
             'skia_lib.gyp:skia_lib',
             'flags.gyp:flags',
             'jsoncpp.gyp:jsoncpp',
             'gputest.gyp:skgputest',
         ],
     }]
 }