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:

   * Fixes to the spec.
   * Change of code length code order.
   * Use a 2-level Huffman lookup table in the decoder.
   * Faster uncompressed meta-block decoding.
   * Optimized encoding of the Huffman code.
   * Detection of UTF-8 input encoding.
   * UTF-8 based literal cost modeling for improved
     backward reference selection.

brotli/enc/bit_cost.h

@@ -93,7 +93,7 @@ static inline int HuffmanBitCost(const uint8_t* depth, int length) {
   cost[17] += 3;
 
   int tree_size = 0;
-  int bits = 6 + 3 * max_depth;  // huffman tree of huffman tree cost
+  int bits = 6 + 2 * max_depth;  // huffman tree of huffman tree cost
   for (int i = 0; i < kCodeLengthCodes; ++i) {
     bits += histogram[i] * cost[i];  // huffman tree bit cost
     tree_size += histogram[i];