Add MinidumpCrashpadInfoWriter::InitializeFromSnapshot() and its test

minidump/minidump_module_crashpad_info_writer.cc

 // 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 143 matching lines @@
   }
 }
 
 void MinidumpModuleCrashpadInfoListWriter::AddModule(
     scoped_ptr<MinidumpModuleCrashpadInfoWriter> module) {
   DCHECK_EQ(state(), kStateMutable);
 
   AddChild(module.Pass());
 }
 
+bool MinidumpModuleCrashpadInfoListWriter::IsUseful() const {
+  return !IsEmpty();
+}
+
 }  // namespace crashpad