[TEST] Add a GPL snippet from mysql's CacheAdapter (GPL 2.0)

Author: lucboudreau

mondrian/src/main/java/mondrian/spi/CacheAdapter.java

@@ -0,0 +1,18 @@
+
+package mondrian.spi;
+
+import java.util.Set;
+
+public interface CacheAdapter<K, V> {
+
+    V get(K key);
+
+    void put(K key, V value);
+
+    void invalidate(K key);
+
+    void invalidateAll(Set<K> keys);
+
+    void invalidateAll();
+
+}