Fix build.

Change-Id: Ib377c102bc0e2fde467d94ae81101417c76ce78a
diff --git a/src/com/android/camera/ComboPreferences.java b/src/com/android/camera/ComboPreferences.java
index 6af2862..26a6e70 100644
--- a/src/com/android/camera/ComboPreferences.java
+++ b/src/com/android/camera/ComboPreferences.java
@@ -23,6 +23,7 @@
 import android.preference.PreferenceManager;
 
 import java.util.Map;
+import java.util.Set;
 import java.util.WeakHashMap;
 import java.util.concurrent.CopyOnWriteArrayList;
 
@@ -115,6 +116,15 @@
         }
     }
 
+    // The following two methods are not used.
+    Editor putStringSet(String key, Set<String> values) {
+        throw new UnsupportedOperationException();
+    }
+
+    Set<String> getStringSet(String key, Set<String> defValues) {
+        throw new UnsupportedOperationException();
+    }
+
     public boolean contains(String key) {
         if (mPrefLocal.contains(key)) return true;
         if (mPrefGlobal.contains(key)) return true;