Implement simple dictionary decay.

Groundwork and implement simple decay.
Increment probability when typed and decrement probability
at GC.

Bug: 6669677

Change-Id: Ib12caead0cbeef4ce7808fe8ac0b00ee331523fe
diff --git a/native/jni/Android.mk b/native/jni/Android.mk
index 0594ddf..36afea5 100644
--- a/native/jni/Android.mk
+++ b/native/jni/Android.mk
@@ -85,6 +85,7 @@
     $(addprefix suggest/policyimpl/dictionary/utils/, \
         buffer_with_extendable_buffer.cpp \
         byte_array_utils.cpp \
+        decaying_utils.cpp \
         dict_file_writing_utils.cpp \
         format_utils.cpp) \
     suggest/policyimpl/gesture/gesture_suggest_policy_factory.cpp \