Clear the network service disk cache for each apptest run.

mojo/devtools/common/mojo_test

Index: mojo/devtools/common/mojo_test
diff --git a/mojo/devtools/common/mojo_test b/mojo/devtools/common/mojo_test
index 8f06f4254e552d8827897fe7504bf9b5bfc300f3..f3fa0d033d3eb8e64b93e9e38089f5fe584cd21b 100755
--- a/mojo/devtools/common/mojo_test
+++ b/mojo/devtools/common/mojo_test
@@ -50,6 +50,7 @@ Any arguments not recognized by the script will be passed on as shell arguments.
 _logger = logging.getLogger()
 
 _CACHE_SERVICE_URL = 'mojo:url_response_disk_cache'
+_NETWORK_SERVICE_URL = 'mojo:network_service'
 
 
 def main():
@@ -68,9 +69,11 @@ def main():
       # We need root to have the stdout of the shell available on the host.
       config.require_root = True
     shell, common_shell_args = shell_arguments.get_shell(config, shell_args)
-    # Tests must be reproducible. Start with an empty cache.
+    # Tests must be reproducible, start with empty caches.
     common_shell_args.append(
         "--args-for=%s %s" % (_CACHE_SERVICE_URL, "--clear"))
+    common_shell_args.append(
+        "--args-for=%s %s" % (_NETWORK_SERVICE_URL, "--clear"))
   except shell_config.ShellConfigurationException as e:
     print e
     return 1