Add gpu implementation of OverdrawXfermode

gyp/dm.gypi

 # Copyright 2015 Google Inc.
 #
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 # GYP for "dm" (Diamond Master, a.k.a Dungeon master, a.k.a GM 2).
 {
   'include_dirs': [
     '../dm',
     '../gm',
     '../include/private',
@@ skipping 26 matching lines @@
   ],
   'sources': [
     '../dm/DM.cpp',
     '../dm/DMSrcSink.cpp',
     '../dm/DMJsonWriter.cpp',
     '../gm/gm.cpp',
 
     '../src/utils/debugger/SkDebugCanvas.cpp',
     '../src/utils/debugger/SkDrawCommand.cpp',
     '../src/utils/debugger/SkObjectParser.cpp',
+    '../src/utils/debugger/SkOverdrawMode.h',
+    '../src/utils/debugger/SkOverdrawMode.cpp',
   ],
   'conditions': [
     [ 'skia_gpu == 1', {
       'dependencies': [ 'gputest.gyp:skgputest' ],
     }],
   ],
 }