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

snapshot/test/test_cpu_context.h

Index: snapshot/test/test_cpu_context.h
diff --git a/snapshot/test/test_cpu_context.h b/snapshot/test/test_cpu_context.h
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index 0000000000000000000000000000000000000000..0de2497abde2bd9e29e84971dfa90b61e0581267
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+++ b/snapshot/test/test_cpu_context.h
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+// 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,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#ifndef CRASHPAD_SNAPSHOT_TEST_TEST_CPU_CONTEXT_H_
+#define CRASHPAD_SNAPSHOT_TEST_TEST_CPU_CONTEXT_H_
+
+#include <stdint.h>
+
+#include "snapshot/cpu_context.h"
+
+namespace crashpad {
+namespace test {
+
+//! \brief Initializes a context structure for testing.
+//!
+//! Initialization is compatible with the initialization used by minidump
+//! context test initialization functions such as InitializeMinidumpContextX86()
+//! and InitializeMinidumpContextAMD64() for identical \a seed values.
+//!
+//! \param[out] context The structure to initialize.
+//! \param[in] seed The seed value. Initializing two context structures of the
+//!     same type with identical seed values should produce identical context
+//!     structures. Initialization with a different seed value should produce
+//!     a different context structure. If \a seed is `0`, \a context is zeroed
+//!     out entirely except for the CPUContext::architecture field, which will
+//!     identify the context type. If \a seed is nonzero, \a context will be
+//!     populated entirely with nonzero values.
+//!
+//! \{
+void InitializeCPUContextX86(CPUContext* context, uint32_t seed);
+void InitializeCPUContextX86_64(CPUContext* context, uint32_t seed);
+//! \}
+
+//! \brief Initializes an `fxsave` context substructure for testing.
+//!
+//! \param[out] fxsave The structure to initialize.
+//! \param[in,out] seed The seed value. Initializing two `fxsave` structures of
+//!     the same type with identical seed values should produce identical
+//!     structures. Initialization with a different seed value should produce
+//!     a different `fxsave` structure. If \a seed is `0`, \a fxsave is zeroed
+//!     out entirely. If \a seed is nonzero, \a fxsave will be populated
+//!     entirely with nonzero values. \a seed will be updated by this function
+//!     to allow the caller to perform subsequent initialization of the context
+//!     structure containing \a fxsave.
+//!
+//! \{
+void InitializeCPUContextX86Fxsave(
+    CPUContextX86::Fxsave* fxsave, uint32_t* seed);
+void InitializeCPUContextX86_64Fxsave(
+    CPUContextX86_64::Fxsave* fxsave, uint32_t* seed);
+//! \}
+
+}  // namespace test
+}  // namespace crashpad
+
+#endif  // CRASHPAD_SNAPSHOT_TEST_TEST_CPU_CONTEXT_H_