Add brotli content-encoding filter.

net/filter/brotli_filter.h

+// Copyright 2015 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.
+
+// BrotliFilter applies Brotli content decoding to a data
+// stream. Brotli format specification:
+// http://www.ietf.org/id/draft-alakuijala-brotli
+//
+// BrotliFilter is a subclass of Filter. See the latter's header file filter.h
+// for sample usage.
+
+#ifndef NET_FILTER_BROTLI_FILTER_H_
+#define NET_FILTER_BROTLI_FILTER_H_
+
+#include "base/basictypes.h"
+#include "base/memory/scoped_ptr.h"
+#include "net/filter/filter.h"
+
+struct BrotliStateStruct;
+
+namespace net {
+
+class BrotliFilter : public Filter {
+ public:
+  ~BrotliFilter() override;
+
+  // Initializes filter decoding mode and internal control blocks.
+  // The function returns true if success and false otherwise.
+  // The filter can only be initialized once.
+  bool InitDecoding();
+
+  // Decodes the pre-filter data and writes the output into the dest_buffer
+  // passed in.
+  // The function returns FilterStatus. See filter.h for its description.
+  //
+  // Upon entry, *dest_len is the total size (in number of chars) of the
+  // destination buffer. Upon exit, *dest_len is the actual number of chars
+  // written into the destination buffer.
+  //
+  // This function will fail if there is no pre-filter data in the
+  // stream_buffer_. On the other hand, *dest_len can be 0 upon successful

[xunjieli, 2015/11/17 16:16:12]

nit: Please surround the variables using pipes. 
e.g. |stream_buffer_| and |*dest_len|

[eustas, 2015/11/17 17:57:21]

Surely. Done.

+  // return. For example, decompressor may process some pre-filter data
+  // but not produce output yet.
+  FilterStatus ReadFilteredData(char* dest_buffer, int* dest_len) override;
+
+ private:
+  enum DecodingStatus {
+    DECODING_UNINITIALIZED,
+    DECODING_IN_PROGRESS,
+    DECODING_DONE,
+    DECODING_ERROR
+  };
+
+  // Only to be instantiated by Filter::Factory.
+  BrotliFilter(FilterType type);
+  friend class Filter;
+
+  bool CheckBrotliHeader();
+
+  // Tracks the status of decoding.
+  // This variable is initialized by InitDecoding and updated only by
+  // ReadFilteredData.
+  DecodingStatus decoding_status_;
+
+  scoped_ptr<BrotliStateStruct> brotli_state_;
+
+  DISALLOW_COPY_AND_ASSIGN(BrotliFilter);
+};
+
+}  // namespace net
+
+#endif  // NET_FILTER_BROTLI_FILTER_H__