add ImageGenerator::NewFromData to porting layer

gyp/images.gyp

 # GYP file for images project.
 {
   'targets': [
     {
       'target_name': 'images',
       'product_name': 'skia_images',
       'type': 'static_library',
       'standalone_static_library': 1,
       'dependencies': [
         'core.gyp:*',
@@ skipping 52 matching lines @@
         '../src/images/SkImageEncoder.cpp',
         '../src/images/SkImageEncoder_Factory.cpp',
         '../src/images/SkImageEncoder_argb.cpp',
         '../src/images/SkJpegUtility.cpp',
         '../src/images/SkMovie.cpp',
         '../src/images/SkMovie_gif.cpp',
         '../src/images/SkPageFlipper.cpp',
         '../src/images/SkScaledBitmapSampler.cpp',
         '../src/images/SkScaledBitmapSampler.h',
 
+        '../src/ports/SkImageGenerator_skia.cpp',
+
         '../src/ports/SkImageDecoder_CG.cpp',
         '../src/ports/SkImageDecoder_WIC.cpp',
       ],
       'conditions': [
         [ 'skia_os == "win"', {
           'sources!': [
             '../src/images/SkImageDecoder_FactoryDefault.cpp',
             '../src/images/SkImageDecoder_libgif.cpp',
             '../src/images/SkImageDecoder_libpng.cpp',
             '../src/images/SkMovie_gif.cpp',
@@ skipping 78 matching lines @@
         }],
       ],
       'direct_dependent_settings': {
         'include_dirs': [
           '../include/images',
         ],
       },
     },
   ],
 }