Add brotli compressor

This commit is for the encoder for brotli compression format.
Brotli is a generic byte-level compression algorithm.

brotli/enc/literal_cost.h

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+// Copyright 2013 Google Inc. All Rights Reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+// Literal cost model to allow backward reference replacement to be efficient.
+
+#ifndef BROTLI_ENC_LITERAL_COST_H_
+#define BROTLI_ENC_LITERAL_COST_H_
+
+#include <stddef.h>
+#include <stdint.h>
+
+namespace brotli {
+
+// Input: length of data, and the bytes.
+// Output: estimate of how many bits the literal will take entropy coded.
+void EstimateBitCostsForLiterals(size_t len, const uint8_t *data, float *cost);
+
+}  // namespace brotli
+
+#endif  // BROTLI_ENC_LITERAL_COST_H_