Rename PrevWordsInfo to NgramContext.

Bug: 14425059
Change-Id: Id06a71681fa8b5e589e29fba10fe5c1cfed66984
diff --git a/java/proguard.flags b/java/proguard.flags
index 35b3ac3..0c5ad9f 100644
--- a/java/proguard.flags
+++ b/java/proguard.flags
@@ -19,6 +19,6 @@
 # to preserve changing those methods' signature.
 -keep class com.android.inputmethod.latin.AssetFileAddress
 -keep class com.android.inputmethod.latin.Dictionary
--keep class com.android.inputmethod.latin.PrevWordsInfo
+-keep class com.android.inputmethod.latin.NgramContext
 -keep class com.android.inputmethod.latin.makedict.ProbabilityInfo
 -keep class com.android.inputmethod.latin.utils.LanguageModelParam