Add MinidumpMemoryListWriter::AddFromSnapshot(), everything downstream and its test

snapshot/mac/memory_snapshot_mac.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 34 matching lines @@
   return address_;
 }
 
 size_t MemorySnapshotMac::Size() const {
   INITIALIZATION_STATE_DCHECK_VALID(initialized_);
   return size_;
 }
 
 bool MemorySnapshotMac::Read(Delegate* delegate) const {
   INITIALIZATION_STATE_DCHECK_VALID(initialized_);
+
+  if (size_ == 0) {
+    return delegate->MemorySnapshotDelegateRead(nullptr, size_);
+  }
+
   scoped_ptr<uint8_t[]> buffer(new uint8_t[size_]);
   if (!process_reader_->Memory()->Read(address_, size_, buffer.get())) {
     return false;
   }
   return delegate->MemorySnapshotDelegateRead(buffer.get(), size_);
 }
 
 }  // namespace internal
 }  // namespace crashpad