Fetch: Make Headers' constructor match the current spec IDL.

third_party/WebKit/LayoutTests/http/tests/fetch/script-tests/request.js

Index: third_party/WebKit/LayoutTests/http/tests/fetch/script-tests/request.js
diff --git a/third_party/WebKit/LayoutTests/http/tests/fetch/script-tests/request.js b/third_party/WebKit/LayoutTests/http/tests/fetch/script-tests/request.js
index 107c0daaa3d5d130ddbc5c804a7d6f2f4721c2de..0ce4e2d8ce6e99bd4bcd71e9b9c94adde6200e6f 100644
--- a/third_party/WebKit/LayoutTests/http/tests/fetch/script-tests/request.js
+++ b/third_party/WebKit/LayoutTests/http/tests/fetch/script-tests/request.js
@@ -129,6 +129,13 @@ test(function() {
                   'Request.headers should match');
     assert_equals(request3.headers.getAll('X-Fetch-Bar')[0], 'bar',
                   'Request.headers should match');
+    var request4 = new Request(request, {headers: undefined});
+    assert_equals(request4.headers.getAll('X-Fetch-Foo')[0], 'foo1',
+                  'Request.headers should match');
+    assert_equals(request4.headers.getAll('X-Fetch-Foo')[1], 'foo2',
+                  'Request.headers should match');
+    assert_equals(request4.headers.getAll('X-Fetch-Bar')[0], 'bar',
+                  'Request.headers should match');
   }, 'Request header test');
 
 test(function() {
@@ -682,7 +689,7 @@ async_test(function(t) {
 
 test(function() {
     // https://fetch.spec.whatwg.org/#dom-request
-    // Step 20:
+    // Step 32:
     // Fill r's Headers object with headers. Rethrow any exceptions.
     INVALID_HEADER_NAMES.forEach(function(name) {
         assert_throws(