Add a variable-length header region to the binary format.

Also bump up the format version to 2.

Bug: 5686638
Change-Id: I3aafdd7e42c422202122998ec093280051aa8e07
diff --git a/native/src/unigram_dictionary.cpp b/native/src/unigram_dictionary.cpp
index 155bdcb..0b646d1 100644
--- a/native/src/unigram_dictionary.cpp
+++ b/native/src/unigram_dictionary.cpp
@@ -38,8 +38,7 @@
 UnigramDictionary::UnigramDictionary(const uint8_t* const streamStart, int typedLetterMultiplier,
         int fullWordMultiplier, int maxWordLength, int maxWords, int maxProximityChars,
         const bool isLatestDictVersion)
-    : DICT_ROOT(streamStart + NEW_DICTIONARY_HEADER_SIZE),
-    MAX_WORD_LENGTH(maxWordLength), MAX_WORDS(maxWords),
+    : DICT_ROOT(streamStart), MAX_WORD_LENGTH(maxWordLength), MAX_WORDS(maxWords),
     MAX_PROXIMITY_CHARS(maxProximityChars), IS_LATEST_DICT_VERSION(isLatestDictVersion),
     TYPED_LETTER_MULTIPLIER(typedLetterMultiplier), FULL_WORD_MULTIPLIER(fullWordMultiplier),
       // TODO : remove this variable.