Add a simple fetch API test.

LayoutTests/http/tests/fetch/PRESUBMIT.py

Index: LayoutTests/http/tests/fetch/PRESUBMIT.py
diff --git a/LayoutTests/http/tests/fetch/PRESUBMIT.py b/LayoutTests/http/tests/fetch/PRESUBMIT.py
index b464de7eee173278fec2f674ac412da8c273bb38..b39e02b6fa3a69a9a24ac90b6cd2caa679be83e4 100644
--- a/LayoutTests/http/tests/fetch/PRESUBMIT.py
+++ b/LayoutTests/http/tests/fetch/PRESUBMIT.py
@@ -14,10 +14,11 @@ import re
 
 def missing_files(scripts_path, top_path, worker_path):
     for script in os.listdir(scripts_path):
+        if script.startswith('.') or not script.endswith('.js'):
+            continue
         basename = re.sub(r'\.js$', '.html', os.path.basename(script))
-        window_path = os.path.join(top_path, basename)
-        worker_path = os.path.join(worker_path, basename)
-        for path in [window_path, worker_path]:
+        for path in [os.path.join(top_path, basename),
+                     os.path.join(worker_path, basename)]:
             if not os.path.exists(path):
                 yield path