Add gpu implementation of OverdrawXfermode

gyp/debugger.gyp

 # Copyright 2015 Google Inc.
 #
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 {
   'variables': {
     'skia_warnings_as_errors': 0,
     'conditions': [
       [ 'skia_os in ["linux", "freebsd", "openbsd", "solaris", "chromeos"]', {
         # Use the systemwide Qt libs by default
@@ skipping 83 matching lines @@
         '<@(qt_includes)',
       ],
       'sources': [
         '../debugger/SkDebugger.cpp',
         '../src/utils/debugger/SkDebugCanvas.h',
         '../src/utils/debugger/SkDebugCanvas.cpp',
         '../src/utils/debugger/SkDrawCommand.h',
         '../src/utils/debugger/SkDrawCommand.cpp',
         '../src/utils/debugger/SkObjectParser.h',
         '../src/utils/debugger/SkObjectParser.cpp',
+        '../src/utils/debugger/SkOverdrawMode.h',
+        '../src/utils/debugger/SkOverdrawMode.cpp',
         '../debugger/debuggermain.cpp',
         '../debugger/QT/SkDebuggerGUI.cpp',
         '../debugger/QT/SkDebuggerGUI.h',
         '../debugger/QT/SkDrawCommandGeometryWidget.h',
         '../debugger/QT/SkDrawCommandGeometryWidget.cpp',
         '../debugger/QT/SkCanvasWidget.cpp',
         '../debugger/QT/SkCanvasWidget.h',
         '../debugger/QT/SkInspectorWidget.h',
         '../debugger/QT/SkInspectorWidget.cpp',
         '../debugger/QT/SkListWidget.h',
@@ skipping 50 matching lines @@
           'outputs': [ '<(moc_gen_dir)/moc_<(RULE_INPUT_ROOT).cpp' ],
           'action': [ '<(qt_moc)', '-DSK_SUPPORT_GPU=<(skia_gpu)',
                       '<(RULE_INPUT_PATH)',
                       '-o', '<(moc_gen_dir)/moc_<(RULE_INPUT_ROOT).cpp' ],
           'message': 'Generating <(RULE_INPUT_ROOT).cpp.',
         },
       ],
     },
   ],
 }