Add toString() method to Keyboard

Change-Id: I74c8f006323ed78ec67414fd17849ab40966968e
diff --git a/java/src/com/android/inputmethod/keyboard/Keyboard.java b/java/src/com/android/inputmethod/keyboard/Keyboard.java
index 3abe890..9198500 100644
--- a/java/src/com/android/inputmethod/keyboard/Keyboard.java
+++ b/java/src/com/android/inputmethod/keyboard/Keyboard.java
@@ -219,6 +219,11 @@
         return code >= CODE_SPACE;
     }
 
+    @Override
+    public String toString() {
+        return mId.toString();
+    }
+
     public static class Params {
         public KeyboardId mId;
         public int mThemeId;