Revert of remove unused SkAvoidXfermode

gyp/SampleApp.gyp

 #
 {
   'variables': {
     #manually set sample_pdf_file_viewer to 1 to have the PdfViewer in SampleApp
     'sample_pdf_file_viewer%': 0,
   },
   'targets': [
     {
       'target_name': 'SampleApp',
       'type': 'executable',
@@ skipping 20 matching lines @@
         '../samplecode/OverView.h',
         '../samplecode/Sample2PtRadial.cpp',
         '../samplecode/SampleAAClip.cpp',
         '../samplecode/SampleAARects.cpp',
         '../samplecode/SampleAARectModes.cpp',
         '../samplecode/SampleAll.cpp',
         '../samplecode/SampleAnimator.cpp',
         '../samplecode/SampleAnimBlur.cpp',
         '../samplecode/SampleApp.cpp',
         '../samplecode/SampleArc.cpp',
+        '../samplecode/SampleAvoid.cpp',
         '../samplecode/SampleBigBlur.cpp',
         '../samplecode/SampleBigGradient.cpp',
         '../samplecode/SampleBitmapRect.cpp',
         '../samplecode/SampleBlur.cpp',
         '../samplecode/SampleCamera.cpp',
         '../samplecode/SampleChart.cpp',
         '../samplecode/SampleCircle.cpp',
         '../samplecode/SampleClock.cpp',
         '../samplecode/SampleClip.cpp',
         '../samplecode/SampleCode.h',
@@ skipping 250 matching lines @@
         }],
       ],
       'msvs_settings': {
         'VCLinkerTool': {
           'SubSystem': '2',
         },
       },
     },
   ],
 }