Updates to Brotli compression format, decoder and encoder

This commit contains a batch of changes that were made to the Brotli
compression algorithm in the last month. Most important changes:

   * Updated spec
   * Changed Huffman code length alphabet to use run length codes more
     efficiently, based on a suggestion by Robert Obryk
   * Changed encoding of the number of Huffman code lengths (HLEN)
   * Changed encoding of the number of Huffman trees (NTREES)
   * Added support for uncompressed meta-blocks

brotli/enc/encode.h

@@ -39,6 +39,7 @@ class BrotliCompressor {
   // written.
   void WriteMetaBlock(const size_t input_size,
                       const uint8_t* input_buffer,
+                      const bool is_last,
                       size_t* encoded_size,
                       uint8_t* encoded_buffer);