Add MinidumpSystemInfoWriter::InitializeFromSnapshot() and its test

snapshot/system_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 61 matching lines @@
   //! ProcessSnapshot::System(). This renders one aspect of this method’s return
   //! value a process attribute rather than a system attribute, but it’s defined
   //! here rather than in ProcessSnapshot because the CPU architecture is a
   //! better conceptual fit for the system abstraction alongside these other
   //! related methods.
   virtual CPUArchitecture GetCPUArchitecture() const = 0;
 
   //! \brief Returns the snapshot system’s CPU revision.
   //!
   //! For x86-family CPUs (including x86_64 and 32-bit x86), this is the CPU
-  //! family ID value from `cpuid 1` `eax`, adjusted to take the extended family
-  //! ID into account.
+  //! family, model, and stepping ID values from `cpuid 1` `eax`. The family and
+  //! model values are adjusted to take the extended family and model IDs into
+  //! account. These values are encoded in this method’s return value with the
+  //! family in the high high 16 bits, the model in the next 8 bits, and the
+  //! stepping in the low 8 bits.
   //!
   //! \return A CPU architecture-specific value identifying the CPU revision.
   virtual uint32_t CPURevision() const = 0;
 
   //! \brief Returns the total number of CPUs present in the snapshot system.
   virtual uint8_t CPUCount() const = 0;
 
   //! \brief Returns the vendor of the snapshot system’s CPUs.
   //!
   //! For x86-family CPUs (including x86_64 and 32-bit x86), this is the CPU
@@ skipping 161 matching lines @@
   virtual void TimeZone(DaylightSavingTimeStatus* observes_daylight,
                         int* standard_offset_seconds,
                         int* daylight_offset_seconds,
                         std::string* standard_name,
                         std::string* daylight_name) const = 0;
 };
 
 }  // namespace crashpad
 
 #endif  // CRASHPAD_SNAPSHOT_SYSTEM_SNAPSHOT_H_