Add image for dev summit banner.

Change-Id: I0bf233439723b9615d0e5c377a1dca3326c524ff
diff --git a/tools/droiddoc/templates-sdk/assets/css/default.css b/tools/droiddoc/templates-sdk/assets/css/default.css
index d493566..7c0cce9 100644
--- a/tools/droiddoc/templates-sdk/assets/css/default.css
+++ b/tools/droiddoc/templates-sdk/assets/css/default.css
@@ -8795,7 +8795,7 @@
   background-color: #fff;
   background-position: 50% 53%;
   background-size: cover;
-  background-image: url(../../assets/images/home/android_m_hero_1200.jpg);
+  background-image: url(../../images/ads_hero_17@2x.jpg);
   box-sizing: border-box;
   font-size: 16px;
   min-height: 550px;