Add MinidumpSystemInfoWriter::InitializeFromSnapshot() and its test

snapshot/snapshot.gyp

 # Copyright 2014 The Crashpad Authors. All rights reserved.
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
 # you may not use this file except in compliance with the License.
 # You may obtain a copy of the License at
 #
 #     http://www.apache.org/licenses/LICENSE-2.0
 #
 # Unless required by applicable law or agreed to in writing, software
 # distributed under the License is distributed on an "AS IS" BASIS,
@@ skipping 76 matching lines @@
       ],
       'sources': [
         'test/test_cpu_context.cc',
         'test/test_cpu_context.h',
         'test/test_exception_snapshot.cc',
         'test/test_exception_snapshot.h',
         'test/test_memory_snapshot.cc',
         'test/test_memory_snapshot.h',
         'test/test_module_snapshot.cc',
         'test/test_module_snapshot.h',
+        'test/test_system_snapshot.cc',
+        'test/test_system_snapshot.h',
         'test/test_thread_snapshot.cc',
         'test/test_thread_snapshot.h',
       ],
     },
     {
       'target_name': 'snapshot_test',
       'type': 'executable',
       'dependencies': [
         'snapshot',
         '../client/client.gyp:client',
@@ skipping 13 matching lines @@
         'mac/mach_o_image_annotations_reader_test.cc',
         'mac/mach_o_image_reader_test.cc',
         'mac/mach_o_image_segment_reader_test.cc',
         'mac/process_reader_test.cc',
         'mac/process_types_test.cc',
         'mac/system_snapshot_mac_test.cc',
       ],
     },
   ],
 }