Prepare dictionary saving in native code.

java/src/com/android/inputmethod/latin/BinaryDictionary.java

...ve/jni/com_android_inputmethod_latin_BinaryDictionary.cpp

native/jni/src/suggest/core/dictionary/dictionary.cpp

native/jni/src/suggest/core/dictionary/dictionary.h

...est/core/policy/dictionary_structure_with_buffer_policy.h

...onary/dictionary_structure_with_buffer_policy_factory.cpp

...tionary/dictionary_structure_with_buffer_policy_factory.h

...st/policyimpl/dictionary/dynamic_patricia_trie_policy.cpp

...gest/policyimpl/dictionary/dynamic_patricia_trie_policy.h

.../src/suggest/policyimpl/dictionary/patricia_trie_policy.h

.../src/suggest/policyimpl/dictionary/utils/mmapped_buffer.h