[Telemetry] Cause web server to keep resources in memory and thread requests.

tools/telemetry/telemetry/page/page_runner.py

Index: tools/telemetry/telemetry/page/page_runner.py
diff --git a/tools/telemetry/telemetry/page/page_runner.py b/tools/telemetry/telemetry/page/page_runner.py
index d94a6d665a44c0fdbbd9966b3214f3f009e220f1..c9b1898ebee9d07703a5359ae0911da54caff151 100644
--- a/tools/telemetry/telemetry/page/page_runner.py
+++ b/tools/telemetry/telemetry/page/page_runner.py
@@ -307,8 +307,8 @@ class PageRunner(object):
   def _PreparePage(self, page, tab, page_state, test, results):
     parsed_url = urlparse.urlparse(page.url)
     if parsed_url[0] == 'file':
-      dirname, filename = page.url_base_dir_and_file
-      tab.browser.SetHTTPServerDirectory(dirname)
+      serving_dirs, filename = page.serving_dirs_and_file
+      tab.browser.SetHTTPServerDirectory(serving_dirs)
       target_side_url = tab.browser.http_server.UrlOf(filename)
     else:
       target_side_url = page.url