SmartLock: Add back background page, it's still being used for now.

R=khorimoto@chromium.org

Bug: none
Test: none
Cq-Include-Trybots: master.tryserver.chromium.linux:closure_compilation
Change-Id: I3c0983fe0bd562bb0d27ffd723a17fd2a0a5d6f6
Reviewed-on: https://chromium-review.googlesource.com/965271Reviewed-by: Kyle Horimoto <khorimoto@chromium.org>
Commit-Queue: James Hawkins <jhawkins@chromium.org>
Cr-Commit-Position: refs/heads/master@{#543558}

chrome/browser/resources/easy_unlock/manifest.json

@@ -34,6 +34,12 @@
     "systemPrivate"
   ],
 
+  "app": {
+    "background": {
+      "scripts": ["easy_unlock_background.js"]
+    }
+  },
+
   "bluetooth": {
     "socket" : true,
     "low_energy" : true,

chrome/browser/resources/easy_unlock/manifest_signin.json

@@ -25,6 +25,12 @@
     "systemPrivate"
   ],
 
+  "app": {
+    "background": {
+      "scripts": ["easy_unlock_background.js"]
+    }
+  },
+
   "bluetooth": {
     "socket" : true,
     "low_energy" : true,