Use PrevWordsInfo for get/add/remove n-gram(bigram) entry.

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

...m/android/inputmethod/latin/ContactsBinaryDictionary.java

...id/inputmethod/latin/DictionaryFacilitatorForSuggest.java

...android/inputmethod/latin/ExpandableBinaryDictionary.java

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

...c/com/android/inputmethod/latin/UserBinaryDictionary.java

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

.../com/android/inputmethod/latin/inputlogic/InputLogic.java

...utmethod/latin/personalization/UserHistoryDictionary.java

...com/android/inputmethod/latin/utils/DistracterFilter.java

...roid/inputmethod/latin/BinaryDictionaryDecayingTests.java

.../com/android/inputmethod/latin/BinaryDictionaryTests.java

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

...m/android/inputmethod/latin/makedict/Ver4DictEncoder.java

...hod/latin/personalization/UserHistoryDictionaryTests.java