Add static domain security state generator tool.

net/tools/domain_security_preload_generator/bit_writer.h

+// Copyright (c) 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef NET_TOOLS_DOMAIN_SECURITY_PRELOAD_GENERATOR_BIT_WRITER_H_
+#define NET_TOOLS_DOMAIN_SECURITY_PRELOAD_GENERATOR_BIT_WRITER_H_
+
+#include <stdint.h>
+
+#include <vector>
+
+namespace net {
+
+// BitWriter acts as a buffer to which bits can be written. The bits are stored
+// as bytes in a vector. BitWriter will buffer bytes. When the buffer contains
+// 8 bits they will be appended to the vector automaticly.

[agl, 2016/12/06 18:51:34]

typo.

[martijnc, 2016/12/07 22:37:53]

Fixed.

+class BitWriter {
+ public:
+  BitWriter();
+  ~BitWriter();
+
+  // Append |bit| to the end of the buffer.
+  void WriteBit(uint8_t bit);
+
+  // Append the last |number_of_bits| of |bits| to the end of the buffer.

[agl, 2016/12/06 18:51:34]

does "last" mean "least-significant"?

[martijnc, 2016/12/07 22:37:53]

Yes, clarified in the comment.

+  void WriteBits(uint32_t bits, uint8_t number_of_bits);
+
+  // Appends the buffered bits in |current_byte_| to the |bytes_| vector. When
+  // there are less than 8 bits in the buffer, the empty bits will be filled
+  // with zero's.
+  void Close();

[agl, 2016/12/06 18:51:34]

I think Close would be better named Flush, since it's possible to continue using
the object afterwards.

[martijnc, 2016/12/07 22:37:53]

Renamed.

+  uint32_t position() const { return position_; }
+
+  // Returns a reference to the |bytes_| buffer of this writer. Make sure to
+  // call Close() so that the buffered bits are written to |bytes_| as well.
+  const std::vector<uint8_t>& bytes() const { return bytes_; }
+
+ private:
+  // Returns the minimum number of bits needed to represent |input|.
+  uint8_t BitLength(uint32_t input) const;
+
+  // Buffers bits until it can fill a byte.
+  uint8_t current_byte_;
+
+  // The number of bits currently in |current_byte_|.
+  uint8_t used_;

[agl, 2016/12/06 18:51:34]

I think we're allowed to say " = 0" in class declarations now, which is
preferable to putting them in the constructor. (Although keep the constructor to
save it being emitted in multiple .o files.)

[martijnc, 2016/12/07 22:37:53]

Done.

+
+  // Number of bits in written to this BitWriter.
+  int32_t position_;

[agl, 2016/12/06 18:51:34]

uint32_t (or size_t) to match the return type of |position|.

[martijnc, 2016/12/07 22:37:53]

Done.

+
+  std::vector<uint8_t> bytes_;
+};
+
+}  // namespace net
+
+#endif  // NET_TOOLS_DOMAIN_SECURITY_PRELOAD_GENERATOR_BIT_WRITER_H_