Use the upstream version of libwebp, v0.4.3.

third_party/libwebp/utils/quant_levels.h

Index: third_party/libwebp/utils/quant_levels.h
diff --git a/third_party/libwebp/utils/quant_levels.h b/third_party/libwebp/utils/quant_levels.h
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+++ b/third_party/libwebp/utils/quant_levels.h
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+// Copyright 2011 Google Inc. All Rights Reserved.
+//
+// Use of this source code is governed by a BSD-style license
+// that can be found in the COPYING file in the root of the source
+// tree. An additional intellectual property rights grant can be found
+// in the file PATENTS. All contributing project authors may
+// be found in the AUTHORS file in the root of the source tree.
+// -----------------------------------------------------------------------------
+//
+// Alpha plane quantization utility
+//
+// Author:  Vikas Arora (vikasa@google.com)
+
+#ifndef WEBP_UTILS_QUANT_LEVELS_H_
+#define WEBP_UTILS_QUANT_LEVELS_H_
+
+#include <stdlib.h>
+
+#include "../webp/types.h"
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+// Replace the input 'data' of size 'width'x'height' with 'num-levels'
+// quantized values. If not NULL, 'sse' will contain the sum of squared error.
+// Valid range for 'num_levels' is [2, 256].
+// Returns false in case of error (data is NULL, or parameters are invalid).
+int QuantizeLevels(uint8_t* const data, int width, int height, int num_levels,
+                   uint64_t* const sse);
+
+#ifdef __cplusplus
+}    // extern "C"
+#endif
+
+#endif  /* WEBP_UTILS_QUANT_LEVELS_H_ */