Add MinidumpContextWriter::CreateFromSnapshot(), everything downstream, and its test

minidump/minidump_context_writer.h

Index: minidump/minidump_context_writer.h
diff --git a/minidump/minidump_context_writer.h b/minidump/minidump_context_writer.h
index 070f3cff7d8ae19bd059cff2cde7938292b4b85e..e48650e32c8c2691a2f1bda25c4b3f0768ca9ab7 100644
--- a/minidump/minidump_context_writer.h
+++ b/minidump/minidump_context_writer.h
@@ -18,17 +18,34 @@
 #include <sys/types.h>
 
 #include "base/basictypes.h"
+#include "base/memory/scoped_ptr.h"
 #include "minidump/minidump_context.h"
 #include "minidump/minidump_writable.h"
 
 namespace crashpad {
 
+struct CPUContext;
+struct CPUContextX86;
+struct CPUContextX86_64;
+
 //! \brief The base class for writers of CPU context structures in minidump
 //!     files.
 class MinidumpContextWriter : public internal::MinidumpWritable {
  public:
   ~MinidumpContextWriter() override;
 
+  //! \brief Creates a MinidumpContextWriter based on \a context_snapshot.
+  //!
+  //! \param[in] context_snapshot The context snapshot to use as source data.
+  //!
+  //! \return A MinidumpContextWriter subclass, such as MinidumpContextWriterX86
+  //!     or MinidumpContextWriterAMD64, appropriate to the CPU type of \a
+  //!     context_snapshot. The returned object is initialized using the source
+  //!     data in \a context_snapshot. If \a context_snapshot is an unknown CPU
+  //!     type’s context, logs a message and returns `nullptr`.
+  static scoped_ptr<MinidumpContextWriter> CreateFromSnapshot(
+      const CPUContext* context_snapshot);
+
  protected:
   MinidumpContextWriter() : MinidumpWritable() {}
 
@@ -52,6 +69,15 @@ class MinidumpContextX86Writer final : public MinidumpContextWriter {
   MinidumpContextX86Writer();
   ~MinidumpContextX86Writer() override;
 
+  //! \brief Initializes the MinidumpContextX86 based on \a context_snapshot.
+  //!
+  //! \param[in] context_snapshot The context snapshot to use as source data.
+  //!
+  //! \note Valid in #kStateMutable. No mutation of context() may be done before
+  //!     calling this method, and it is not normally necessary to alter
+  //!     context() after calling this method.
+  void InitializeFromSnapshot(const CPUContextX86* context_snapshot);
+
   //! \brief Returns a pointer to the context structure that this object will
   //!     write.
   //!
@@ -83,6 +109,15 @@ class MinidumpContextAMD64Writer final : public MinidumpContextWriter {
   MinidumpContextAMD64Writer();
   ~MinidumpContextAMD64Writer() override;
 
+  //! \brief Initializes the MinidumpContextAMD64 based on \a context_snapshot.
+  //!
+  //! \param[in] context_snapshot The context snapshot to use as source data.
+  //!
+  //! \note Valid in #kStateMutable. No mutation of context() may be done before
+  //!     calling this method, and it is not normally necessary to alter
+  //!     context() after calling this method.
+  void InitializeFromSnapshot(const CPUContextX86_64* context_snapshot);
+
   //! \brief Returns a pointer to the context structure that this object will
   //!     write.
   //!