libwebp: update to 0.4.1

third_party/libwebp/utils/huffman_encode.h

Index: third_party/libwebp/utils/huffman_encode.h
diff --git a/third_party/libwebp/utils/huffman_encode.h b/third_party/libwebp/utils/huffman_encode.h
index ee51c68c9ff7c1cee1978103360612f4377d81c3..91aa18f464559f2bdf330bfc502d004800c7e296 100644
--- a/third_party/libwebp/utils/huffman_encode.h
+++ b/third_party/libwebp/utils/huffman_encode.h
@@ -33,14 +33,26 @@ typedef struct {
   uint16_t* codes;         // Symbol Codes.
 } HuffmanTreeCode;
 
+// Struct to represent the Huffman tree.
+// TODO(vikasa): Add comment for the fields of the Struct.
+typedef struct {
+  uint32_t total_count_;
+  int value_;
+  int pool_index_left_;    // Index for the left sub-tree.
+  int pool_index_right_;   // Index for the right sub-tree.
+} HuffmanTree;
+
 // Turn the Huffman tree into a token sequence.
 // Returns the number of tokens used.
 int VP8LCreateCompressedHuffmanTree(const HuffmanTreeCode* const tree,
                                     HuffmanTreeToken* tokens, int max_tokens);
 
 // Create an optimized tree, and tokenize it.
-int VP8LCreateHuffmanTree(int* const histogram, int tree_depth_limit,
-                          HuffmanTreeCode* const tree);
+// 'buf_rle' and 'huff_tree' are pre-allocated and the 'tree' is the constructed
+// huffman code tree.
+void VP8LCreateHuffmanTree(uint32_t* const histogram, int tree_depth_limit,
+                           uint8_t* const buf_rle, HuffmanTree* const huff_tree,
+                           HuffmanTreeCode* const tree);
 
 #ifdef __cplusplus
 }