Cache API tests: prepopulate cache in deterministic order

Chrome and Firefox differ in the order in which cache keys() are
returned. Chrome orders by according to when the put()s were issued.
Firefox orders by when the body is complete. The test helper
prepopulated_cache_test did not guarantee that these matched, leading
to the tests being flaky in Firefox. This change tweaks the helper so
that the put()s are processed serially so that the order is
deterministic for both.

Spec issue: w3c/ServiceWorker#823
BUG=655479

Review-Url: https://codereview.chromium.org/2806793002
Cr-Commit-Position: refs/heads/master@{#463195}

Author: inexorabletash

third_party/WebKit/LayoutTests/external/wpt/service-workers/cache-storage/resources/test-helpers.js

@@ -141,23 +141,26 @@ var vary_entries = [
 // Run |test_function| with a Cache object and a map of entries. Prior to the
 // call, the Cache is populated by cache entries from |entries|. The latter is
 // expected to be an Object mapping arbitrary keys to objects of the form
-// {request: <Request object>, response: <Response object>}. There's no
-// guarantee on the order in which entries will be added to the cache.
+// {request: <Request object>, response: <Response object>}. Entries are
+// serially added to the cache in the order specified.
 //
 // |test_function| should return a Promise that can be used with promise_test.
 function prepopulated_cache_test(entries, test_function, description) {
   cache_test(function(cache) {
       var p = Promise.resolve();
       var hash = {};
-      return Promise.all(entries.map(function(entry) {
+      entries.forEach(function(entry) {
           hash[entry.name] = entry;
-          return cache.put(entry.request.clone(),
-                           entry.response.clone())
-            .catch(function(e) {
-                assert_unreached(
-                  'Test setup failed for entry ' + entry.name + ': ' + e);
-            });
-        }))
+          p = p.then(function() {
+              return cache.put(entry.request.clone(), entry.response.clone())
+                  .catch(function(e) {
+                      assert_unreached(
+                          'Test setup failed for entry ' + entry.name + ': ' + e
+                      );
+                  });
+          });
+      });
+      return p
         .then(function() {
             assert_equals(Object.keys(hash).length, entries.length);
         })