Add brotli content-encoding filter.

net/filter/filter.h

 // Copyright 2014 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.
 //
 // Filter performs filtering on data streams. Sample usage:
 //
 //   IStream* pre_filter_source;
 //   ...
 //   Filter* filter = Filter::Factory(filter_type, size);
 //   int pre_filter_data_len = filter->stream_buffer_size();
@@ skipping 133 matching lines @@
     FILTER_NEED_MORE_DATA,
     // Read filtered data successfully, and filter reaches the end of the data
     // stream.
     FILTER_DONE,
     // There is an error during filtering.
     FILTER_ERROR
   };
 
   // Specifies type of filters that can be created.
   enum FilterType {
+    FILTER_TYPE_BROTLI,
     FILTER_TYPE_DEFLATE,
     FILTER_TYPE_GZIP,
     FILTER_TYPE_GZIP_HELPING_SDCH,  // Gzip possible, but pass through allowed.
     FILTER_TYPE_SDCH,
     FILTER_TYPE_SDCH_POSSIBLE,  // Sdch possible, but pass through allowed.
     FILTER_TYPE_UNSUPPORTED,
   };
 
   virtual ~Filter();
 
@@ skipping 60 matching lines @@
   // encodings. These fixups require context, which includes whether this
   // response was made to an SDCH request (i.e., an available dictionary was
   // advertised in the GET), as well as the mime type of the content.
   static void FixupEncodingTypes(const FilterContext& filter_context,
                                  std::vector<FilterType>* encoding_types);
 
   // Returns a string describing the FilterTypes implemented by this filter.
   std::string OrderedFilterList() const;
 
  protected:
+  friend class BrotliFilter;

[Ryan Sleevi, 2015/12/17 01:04:40]

^ this strikes me as an anti-pattern, as it represents circular layering. Could
you explain more?

[eustas, 2015/12/17 16:44:54]

For some reason InitBuffer is a private method. I've baked its invocation into
CreateBrotliFilter to have the least amount of added code to filter.cc
Rolled back.

+  friend class BrotliUnitTest;
   friend class GZipUnitTest;
   friend class SdchFilterChainingTest;
   FRIEND_TEST_ALL_PREFIXES(FilterTest, ThreeFilterChain);
 
   explicit Filter(FilterType type_id);
 
   // Filters the data stored in stream_buffer_ and writes the output into the
   // dest_buffer passed in.
   //
   // Upon entry, *dest_len is the total size (in number of chars) of the
@@ skipping 62 matching lines @@
 
   // The filter type this filter was constructed from.
   FilterType type_id_;
 
   DISALLOW_COPY_AND_ASSIGN(Filter);
 };
 
 }  // namespace net
 
 #endif  // NET_FILTER_FILTER_H__