This CL adds client.toDataURL which gets the contents...

utils/utils.gyp

 # Copyright (c) 2009 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 {
   'variables': {
     'chromium_code': 1,
   },
   'includes': [
     '../build/common.gypi',
   ],
   'target_defaults': {
     'include_dirs': [
       '..',
       '../..',
       '../../<(gtestdir)',
     ],
   },
   'targets': [
     {
       'target_name': 'o3dUtils',
       'type': 'static_library',
       'sources': [
+        "cross/base64.cc",
+        "cross/base64.h",
+        "cross/dataurl.cc",
+        "cross/dataurl.h",
         "cross/file_path_utils.cc",
         "cross/file_path_utils.h",
         "cross/file_text_reader.cc",
         "cross/file_text_reader.h",
         "cross/file_text_writer.cc",
         "cross/file_text_writer.h",
         "cross/json_writer.cc",
         "cross/json_writer.h",
         "cross/string_reader.cc",
         "cross/string_reader.h",
         "cross/string_writer.cc",
         "cross/string_writer.h",
         "cross/structured_writer.h",
         "cross/temporary_file.cc",
         "cross/temporary_file.h",
         "cross/text_reader.cc",
         "cross/text_reader.h",
         "cross/text_writer.cc",
         "cross/text_writer.h",
       ],
     },
     {
       'target_name': 'o3dUtilsTest',
       'type': 'none',
       'dependencies': [
         'o3dUtils',
       ],
       'direct_dependent_settings': {
         'sources': [
+          "cross/base64_test.cc",
+          "cross/dataurl_test.cc",
           "cross/file_path_utils_test.cc",
           "cross/file_text_reader_test.cc",
           "cross/json_writer_test.cc",
           "cross/string_reader_test.cc",
           "cross/string_writer_test.cc",
           "cross/temporary_file_test.cc",
         ],
       },
     },
   ],
 }