Implement C path functions

gyp/experimental.gyp

 # GYP file to build experimental directory.
 {
   'targets': [
     {
       'target_name': 'experimental',
       'type': 'static_library',
       'include_dirs': [
         '../include/config',
         '../include/core',
       ],
       'sources': [
         '../experimental/SkSetPoly3To3.cpp',
         '../experimental/SkSetPoly3To3_A.cpp',
         '../experimental/SkSetPoly3To3_D.cpp',
+        '../experimental/sk_surface.h',
+        '../experimental/sk_surface.cpp',
       ],
       'direct_dependent_settings': {
         'include_dirs': [
           '../experimental',
         ],
       },
     },
     {
       'target_name': 'SkiaExamples',
       'type': 'executable',
@@ skipping 45 matching lines @@
             'INFOPLIST_FILE' : '../experimental/SkiaExamples/SkiaExamples-Info.plist',
           },
           'mac_bundle_resources' : [
             '../experimental/SkiaExamples/SkiaExamples.xib'
           ],
         }],
       ],
     }
   ],
 }