Introduce MinidumpWritable, its dependencies, and their tests

util/file/fd_io.h

Index: util/file/fd_io.h
diff --git a/util/file/fd_io.h b/util/file/fd_io.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_UTIL_FILE_FD_IO_H_
+#define CRASHPAD_UTIL_FILE_FD_IO_H_
+
+#include <sys/types.h>
+
+namespace crashpad {
+
+//! \brief Wraps `read()`, retrying when interrupted or following a short read.
+//!
+//! This function reads into \a buffer, stopping only when \a size bytes have
+//! been read or when `read()` returns 0, indicating that end-of-file has been
+//! reached.
+//!
+//! \return The number of bytes read and placed into \a buffer, or `-1` on
+//!     error, with `errno` set appropriately. On error, a portion of \a fd may
+//!     have been read into \a buffer.
+//!
+//! \sa WriteFD
+ssize_t ReadFD(int fd, void* buffer, size_t size);
+
+//! \brief Wraps `write()`, retrying when interrupted or following a short
+//!     write.
+//!
+//! This function writes to \a fd, stopping only when \a size bytes have been
+//! written.
+//!
+//! \return The number of bytes written from \a buffer, or `-1` on error, with
+//!     `errno` set appropriately. On error, a portion of \a buffer may have
+//!     been written to \a fd.
+//!
+//! \sa ReadFD
+ssize_t WriteFD(int fd, const void* buffer, size_t size);
+
+}  // namespace crashpad
+
+#endif  // CRASHPAD_UTIL_FILE_FD_IO_H_