Switch SkPDFStream's internal storage from SkStream to SkData

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 10 matching lines @@
           ],
         }],
       ],
       'include_dirs': [
         '../include/images',
         '../src/lazy',
         # for access to SkErrorInternals.h
         '../src/core/',
         # for access to SkImagePriv.h
         '../src/image/',
-        # So src/ports/SkImageDecoder_CG can access SkStreamHelpers.h
-        '../src/images/',
       ],
       'sources': [
         '../include/images/SkDecodingImageGenerator.h',
         '../include/images/SkForceLinking.h',
         '../src/images/SkJpegUtility.h',
         '../include/images/SkMovie.h',
         '../include/images/SkPageFlipper.h',
 
         '../src/images/bmpdecoderhelper.cpp',
         '../src/images/bmpdecoderhelper.h',
@@ skipping 27 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/images/SkStreamHelpers.cpp',
-        '../src/images/SkStreamHelpers.h',
 
         '../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',
@@ skipping 70 matching lines @@
         }],
       ],
       'direct_dependent_settings': {
         'include_dirs': [
           '../include/images',
         ],
       },
     },
   ],
 }