Create empty ver4 dictionary buffer on memory.

...ve/jni/com_android_inputmethod_latin_BinaryDictionary.cpp

...cture/dictionary_structure_with_buffer_policy_factory.cpp

...mpl/dictionary/structure/v4/content/bigram_dict_content.h

...ictionary/structure/v4/content/probability_dict_content.h

...l/dictionary/structure/v4/content/shortcut_dict_content.h

...mpl/dictionary/structure/v4/content/single_dict_content.h

...ctionary/structure/v4/content/sparse_table_dict_content.h

...ary/structure/v4/content/terminal_position_lookup_table.h

...st/policyimpl/dictionary/structure/v4/ver4_dict_buffers.h

...olicyimpl/dictionary/structure/v4/ver4_dict_constants.cpp

.../policyimpl/dictionary/structure/v4/ver4_dict_constants.h

...mpl/dictionary/structure/v4/ver4_patricia_trie_policy.cpp

...yimpl/dictionary/structure/v4/ver4_patricia_trie_policy.h

...t/policyimpl/dictionary/utils/dict_file_writing_utils.cpp

...est/policyimpl/dictionary/utils/dict_file_writing_utils.h