Add preference demos

b/25639703
b/28468740

Change-Id: I6d78486b4d5164f9b988876adeb7b50377887778
diff --git a/settings.gradle b/settings.gradle
index 252b10d..932a4e6 100644
--- a/settings.gradle
+++ b/settings.gradle
@@ -102,6 +102,9 @@
 include ':support-percent-demos'
 project(':support-percent-demos').projectDir = new File(samplesRoot, 'SupportPercentDemos')
 
+include ':support-preference-demos'
+project(':support-preference-demos').projectDir = new File(samplesRoot, 'SupportPreferenceDemos')
+
 include ':support-transition-demos'
 project(':support-transition-demos').projectDir = new File(samplesRoot, 'SupportTransitionDemos')