Rebuild test history databases when starting up performance_ui_tests.

chrome/test/data/profiles/profile_with_complex_theme/Default/PreferencesTemplate

 {
    "download": {
       "directory_upgrade": true,
       "extensions_to_open": ""
    },
    "extensions": {
       "autoupdate": {
          "next_check": "12894520286433189"
       },
       "settings": {
@@ skipping 33 matching lines @@
                   }
                },
                "version": "1.1"
             },
             "path": "mblmlcbknbnfebdfjnolmcapmdofhmme/1.1",
             "state": 1
          }
       },
       "theme": {
          "id": "mblmlcbknbnfebdfjnolmcapmdofhmme",
-         "pack": "$1/Default/Extensions/mblmlcbknbnfebdfjnolmcapmdofhmme/1.1/Cached Theme.pak"
+         "pack": "$1/Default/Extensions/mblmlcbknbnfebdfjnolmcapmdofhmme/1.1/Cached Theme.pak",
+         "use_system": false
       }
    },
    "profile": {
       "exited_cleanly": true,
       "id": "not-signed-in",
       "name": "Not Signed In",
       "nickname": "not-signed-in"
    },
    "session": {
       "urls_to_restore_on_startup": [  ]
    },
    "spellcheck": {
       "dictionary": "en-US"
    }
 }