Removes fallback from Prefs to LoadExtension on UI thread

chrome/test/data/extensions/bad/Preferences

 {
    "extensions": {
       "settings": {
          "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa": {
             "location": 1,
             "path": "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa/1",
-            "state": 1
+            "state": 1,
+            "manifest": "I am not a manifest"
          },
          "bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb": {
             "location": 1,
             "path": "bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb/1",
             "state": 1
          },
          "bjafgdebaacbbbecmhlhpofkepfkgcpa": {
             "location": 1,
             "path": "bjafgdebaacbbbecmhlhpofkepfkgcpa/1.0",
-            "state": 1
+            "state": 1,
+            "manifest": {
+              "key": "MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQDRS2GUBOUAO5VZ2CMRId/eRR8/e9V42nUvY5XG+0sZ+JDHEjIQdq8qQy7HqdqEpCXKPMSPuMiC2t2HE9/hpL89SblNn3mwYPtSJGQdZvAzuv6SB0oA6jZ66V7+h/k0noGD3Tcu+Ko/vfkt5wCx2uHVK29k5JR/vGr0klaoVezGlwIDAQAB",
+              "version": "1.0",
+              "name": "My extension 3",
+              "content_scripts": [
+                {
+                  "matches": ["http://*/*"]
+                }
+              ]
+            }
          },
             "cccccccccccccccccccccccccccccccc": {
             "location": 1,
             "path": "cccccccccccccccccccccccccccccccc/1.0",
             "state": 1
          }
       }
    }
 }