Switch SkPDFStream's internal storage from SkStream to SkData

gyp/pdf.gyp

 # This file builds the PDF backend.
 {
   'targets': [
     {
       'target_name': 'pdf',
       'product_name': 'skia_pdf',
       'type': 'static_library',
       'standalone_static_library': 1,
       'dependencies': [
         'skia_lib.gyp:skia_lib',
         'skflate.gyp:skflate',
       ],
       'includes': [
         'pdf.gypi',
       ],
       'include_dirs': [
         '../include/pdf',
         '../src/core', # needed to get SkGlyphCache.h and SkTextFormatParams.h
         '../src/pdf',
         '../src/utils', # needed to get SkBitSet.h
+        '../src/images', # needed to get SkStreamHelpers.h
       ],
       'sources': [
         'pdf.gypi', # Makes the gypi appear in IDEs (but does not modify the build).
 
         '../src/doc/SkDocument_PDF.cpp', # Chromium does use this file
       ],
       'conditions': [
         [ 'skia_android_framework', {
             # Add SFTNLY support for PDF (which in turns depends on ICU)
             'include_dirs': [
@@ skipping 13 matching lines @@
         'defines': [
           'SK_SUPPORT_PDF',
         ],
         'include_dirs': [
           '../include/pdf',
         ],
       },
     },
   ],
 }