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

snapshot/memory_snapshot.h

 // 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 21 matching lines @@
   //! data is read, it will be passed to a delegate method.
   class Delegate {
    public:
     virtual ~Delegate() {}
 
     //! \brief Called by MemorySnapshot::Read() to provide data requested by a
     //!     call to that method.
     //!
     //! \param[in] data A pointer to the data that was read. The callee does not
     //!     take ownership of this data. This data is only valid for the
-    //!     duration of the call to this method.
+    //!     duration of the call to this method. This parameter may be `nullptr`
+    //!     if \a size is `0`.
     //! \param[in] size The size of the data that was read.
     //!
     //! \return `true` on success, `false` on failure. MemoryDelegate::Read()
     //!     will use this as its own return value.
     virtual bool MemorySnapshotDelegateRead(void* data, size_t size) = 0;
   };
 
   virtual ~MemorySnapshot() {}
 
   //! \brief The base address of the memory snapshot in the snapshot process’
@@ skipping 14 matching lines @@
   //!
   //! \return `false` on failure, otherwise, the return value of
   //!     Delegate::MemorySnapshotDelegateRead(), which should be `true` on
   //!     success and `false` on failure.
   virtual bool Read(Delegate* delegate) const = 0;
 };
 
 }  // namespace crashpad
 
 #endif  // CRASHPAD_SNAPSHOT_MEMORY_SNAPSHOT_H_