win: Add and use a custom CaptureContext() implementation

util/win/capture_context.h

Index: util/win/capture_context.h
diff --git a/util/win/capture_context.h b/util/win/capture_context.h
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+++ b/util/win/capture_context.h
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+// Copyright 2015 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_CLIENT_CAPTURE_CONTEXT_WIN_H_
+#define CRASHPAD_CLIENT_CAPTURE_CONTEXT_WIN_H_
+
+#include <windows.h>
+
+namespace crashpad {
+
+//! \brief Saves the CPU context.
+//!
+//! The CPU context will be captured as accurately and completely as possible,
+//! containing an atomic snapshot at the point of this function’s return. This
+//! function does not modify any registers.
+//!
+//! This function captures all integer registers as well as the floating-point
+//! and vector (SSE) state. It does not capture debug registers, which are
+//! inaccessible by user code.
+//!
+//! This function is a replacement for `RtlCaptureContext()`, which contains
+//! bugs and limitations. On 32-bit x86, `RtlCaptureContext()` requires that
+//! `ebp` be used as a frame pointer, and returns `ebp`, `esp`, and `eip` out of
+//! sync with the other registers. Both the 32-bit x86 and 64-bit x86_64
+//! versions of `RtlCaptureContext()` capture only the state of the integer
+//! registers, ignoring floating-point and vector state.
+//!
+//! \param[out] context The structure to store the context in.
+//!
+//! \note On x86_64, the value for `rcx` will be populated with the address of
+//!     this function’s argument, as mandated by the ABI.
+void CaptureContext(CONTEXT* context);
+
+}  // namespace crashpad
+
+#endif  // CRASHPAD_CLIENT_CAPTURE_CONTEXT_WIN_H_