make set3DMask virtual, so we can safely notify the shadercontext

gyp/gmslides.gypi

 # include this gypi to include all the golden master slides.
 {
   'include_dirs': [
     '../gm',
     # include dirs needed by particular GMs
     '../src/utils/debugger',
     '../src/images',
     '../src/lazy',
   ],
   'conditions': [
@@ skipping 53 matching lines @@
         '../gm/deviceproperties.cpp',
         '../gm/distantclip.cpp',
         '../gm/displacement.cpp',
         '../gm/downsamplebitmap.cpp',
         '../gm/drawbitmaprect.cpp',
         '../gm/drawlooper.cpp',
         '../gm/dropshadowimagefilter.cpp',
         '../gm/drrect.cpp',
         '../gm/etc1bitmap.cpp',
         '../gm/extractbitmap.cpp',
+        '../gm/emboss.cpp',
         '../gm/emptypath.cpp',
         '../gm/fatpathfill.cpp',
         '../gm/factory.cpp',
         '../gm/filltypes.cpp',
         '../gm/filltypespersp.cpp',
         '../gm/filterbitmap.cpp',
         '../gm/filterindiabox.cpp',
         '../gm/fontcache.cpp',
         '../gm/fontmgr.cpp',
         '../gm/fontscaler.cpp',
@@ skipping 148 matching lines @@
         '../gm/shadertext2.cpp',
         '../gm/shadertext3.cpp',
 
         # TODO(reed): Allocates more memory than Android devices are capable of
         # fulfilling. See http://skbug.com/1978
         '../gm/verylargebitmap.cpp',
       ],
     }],
   ],
 }