[chromedriver] Fix race in navigation tracker.

chrome/test/chromedriver/chrome/navigation_tracker.cc

Index: chrome/test/chromedriver/chrome/navigation_tracker.cc
diff --git a/chrome/test/chromedriver/chrome/navigation_tracker.cc b/chrome/test/chromedriver/chrome/navigation_tracker.cc
index 92de57ab39a60b9f002aa6ca9073ddb0396d5a83..5f5fb3a705b77027d95c9ce3dbf8d3b47379fca2 100644
--- a/chrome/test/chromedriver/chrome/navigation_tracker.cc
+++ b/chrome/test/chromedriver/chrome/navigation_tracker.cc
@@ -150,6 +150,7 @@ Status NavigationTracker::OnCommandSuccess(DevToolsClient* client,
     // been received.
     // If case #3, the URL will be blank if the navigation hasn't been started
     // yet. In that case, expect a load to happen in the future.
+    loading_state_ = kUnknown;
     base::DictionaryValue params;
     params.SetString("expression", "document.URL");
     scoped_ptr<base::DictionaryValue> result;
@@ -158,7 +159,7 @@ Status NavigationTracker::OnCommandSuccess(DevToolsClient* client,
     std::string url;
     if (status.IsError() || !result->GetString("result.value", &url))
       return Status(kUnknownError, "cannot determine loading status", status);
-    if (url.empty())
+    if (loading_state_ == kUnknown && url.empty())
       loading_state_ = kLoading;
   }
   return Status(kOk);