Add an option for the userbility study mode

Change-Id: If41ddfa933f8ade58afa03acbd9536e0477baae8
diff --git a/java/res/values/strings.xml b/java/res/values/strings.xml
index 005fe5e..30b348d 100644
--- a/java/res/values/strings.xml
+++ b/java/res/values/strings.xml
@@ -451,4 +451,6 @@
     <!-- Title for Latin keyboard debug settings activity / dialog -->
     <string name="english_ime_debug_settings" translatable="false">Android keyboard Debug settings</string>
     <string name="prefs_debug_mode" translatable="false">Debug Mode</string>
+    <!-- Title of an option for usability study mode -->
+    <string name="prefs_usability_study_mode">Usability Study Mode</string>
 </resources>
diff --git a/java/res/xml/prefs.xml b/java/res/xml/prefs.xml
index 2ca1af9..d3ac0da 100644
--- a/java/res/xml/prefs.xml
+++ b/java/res/xml/prefs.xml
@@ -117,6 +117,13 @@
             android:persistent="true"
             android:defaultValue="true"
             />
-    </PreferenceCategory>            
+    </PreferenceCategory>
+
+    <CheckBoxPreference
+            android:key="usability_study_mode"
+            android:title="@string/prefs_usability_study_mode"
+            android:persistent="true"
+            android:defaultValue="false"
+            />
 
 </PreferenceScreen>