Fix unit tests by adding @UsedForTesting

Change-Id: I9448b1bfa7bf94039de737725851e63a2921a443
diff --git a/java/src/com/android/inputmethod/latin/BinaryDictionary.java b/java/src/com/android/inputmethod/latin/BinaryDictionary.java
index 83ee982..5bf9bf6 100644
--- a/java/src/com/android/inputmethod/latin/BinaryDictionary.java
+++ b/java/src/com/android/inputmethod/latin/BinaryDictionary.java
@@ -373,8 +373,7 @@
         return getProbabilityNative(mNativeDict, codePoints);
     }
 
-    // TODO: Add a batch process version (isValidBigramMultiple?) to avoid excessive numbers of jni
-    // calls when checking for changes in an entire dictionary.
+    @UsedForTesting
     public boolean isValidBigram(final String word0, final String word1) {
         return getBigramProbability(word0, word1) != NOT_A_PROBABILITY;
     }