Add HpackDecoder3, an adapter using HpackDecoder (in net/http2/hpack/decoder).

net/spdy/hpack/hpack_decoder_interface.h

 // Copyright 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_SPDY_HPACK_HPACK_DECODER_INTERFACE_H_
 #define NET_SPDY_HPACK_HPACK_DECODER_INTERFACE_H_
 
 // HpackDecoderInterface is the base class for HPACK block decoders.
 // HPACK is defined in http://tools.ietf.org/html/rfc7541
 
@@ skipping 10 matching lines @@
 
 class NET_EXPORT_PRIVATE HpackDecoderInterface {
  public:
   virtual ~HpackDecoderInterface() {}
 
   // Called upon acknowledgement of SETTINGS_HEADER_TABLE_SIZE.
   virtual void ApplyHeaderTableSizeSetting(size_t size_setting) = 0;
 
   // If a SpdyHeadersHandlerInterface is provided, the decoder will emit
   // headers to it rather than accumulating them in a SpdyHeaderBlock.
+  // Does not take ownership of the handler, but does use the pointer until
+  // the current HPACK block is completely decoded.
   virtual void HandleControlFrameHeadersStart(
       SpdyHeadersHandlerInterface* handler) = 0;
 
   // Called as HPACK block fragments arrive. Returns false if an error occurred
-  // while decoding the block.
+  // while decoding the block. Does not take ownership of headers_data.
   virtual bool HandleControlFrameHeadersData(const char* headers_data,
                                              size_t headers_data_length) = 0;
 
   // Called after a HPACK block has been completely delivered via
   // HandleControlFrameHeadersData(). Returns false if an error occurred.
   // |compressed_len| if non-null will be set to the size of the encoded
   // buffered block that was accumulated in HandleControlFrameHeadersData(),
   // to support subsequent calculation of compression percentage.
   // Discards the handler supplied at the start of decoding the block.
   // TODO(jamessynge): Determine if compressed_len is needed; it is used to
   // produce UUMA stat Net.SpdyHpackDecompressionPercentage, but only for
   // deprecated SPDY3.
   virtual bool HandleControlFrameHeadersComplete(size_t* compressed_len) = 0;
 
   // Accessor for the most recently decoded headers block. Valid until the next
   // call to HandleControlFrameHeadersData().
   // TODO(birenroy): Remove this method when all users of HpackDecoder specify
   // a SpdyHeadersHandlerInterface.
   virtual const SpdyHeaderBlock& decoded_block() const = 0;
 
   virtual void SetHeaderTableDebugVisitor(
       std::unique_ptr<HpackHeaderTable::DebugVisitorInterface> visitor) = 0;
 
   // Set how much encoded data this decoder is willing to buffer.
+  // TODO(jamessynge): Resolve definition of this value, as it is currently
+  // too tied to a single implementation. We probably want to limit one or more
+  // of these: individual name or value strings, header entries, the entire
+  // header list, or the HPACK block; we probably shouldn't care about the size
+  // of individual transport buffers.
   virtual void set_max_decode_buffer_size_bytes(
       size_t max_decode_buffer_size_bytes) = 0;
 };
 
 }  // namespace net
 
 #endif  // NET_SPDY_HPACK_HPACK_DECODER_INTERFACE_H_