Implement an SkPicture image filter source. This is required for the external-SVG reference feature…

gyp/gmslides.gypi

 # include this gypi to include all the golden master slides.
 {
   'sources': [
     '../gm/aaclip.cpp',
     '../gm/aarectmodes.cpp',
     '../gm/alphagradients.cpp',
     '../gm/androidfallback.cpp',
     '../gm/arcofzorro.cpp',
     '../gm/arithmode.cpp',
     '../gm/beziereffects.cpp',
@@ skipping 87 matching lines @@
     '../gm/offsetimagefilter.cpp',
     '../gm/optimizations.cpp',
     '../gm/ovals.cpp',
     '../gm/patheffects.cpp',
     '../gm/pathfill.cpp',
     '../gm/pathinterior.cpp',
     '../gm/pathopsinverse.cpp',
     '../gm/pathopsskpclip.cpp',
     '../gm/pathreverse.cpp',
     '../gm/perlinnoise.cpp',
+    '../gm/picturesource.cpp',
     '../gm/points.cpp',
     '../gm/poly2poly.cpp',
     '../gm/polygons.cpp',
     '../gm/quadpaths.cpp',
     '../gm/rects.cpp',
     '../gm/rrect.cpp',
     '../gm/rrects.cpp',
     '../gm/roundrects.cpp',
     '../gm/samplerstress.cpp',
     # '../gm/scalebitmap.cpp',
@@ skipping 27 matching lines @@
     '../gm/typeface.cpp',
     '../gm/verttext.cpp',
     '../gm/verttext2.cpp',
     '../gm/verylargebitmap.cpp',
     '../gm/xfermodeimagefilter.cpp',
     '../gm/xfermodes.cpp',
     '../gm/xfermodes2.cpp',
     '../gm/xfermodes3.cpp',
   ],
 }