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:

   * Format change: don't push distances representing static dictionary words to the distance cache.
   * Fix decoder invalid memory access bug caused by building a non-complete Huffman tree.
   * Add a mode parameter to the encoder interface.
   * Use different hashers for text and font mode.
   * Add a heuristics to the hasher for skipping non-compressible data.
   * Exhaustive search of static dictionary during backward reference search.

brotli/enc/backward_references.h

@@ -31,7 +31,8 @@ void CreateBackwardReferences(size_t num_bytes,
                               const float* literal_cost,
                               size_t ringbuffer_mask,
                               const size_t max_backward_limit,
-                              Hasher* hasher,
+                              Hashers* hashers,
+                              Hashers::Type hash_type,
                               std::vector<Command>* commands);
 
 }  // namespace brotli