[Fetch API] Implement combining of Headers with same keys.

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

 if (self.importScripts) {
   importScripts('../resources/fetch-test-helpers.js');
 }
 
 test(function() {
     var expectedValueMap = {
       'content-language': 'ja',
       'content-type': 'text/html; charset=UTF-8',
       'x-fetch-test': 'response test field'
     };
@@ skipping 233 matching lines @@
 
     headers.delete('a');
     headers.set('d', '4');
 
     const keys = [];
     for (let [key, value] of iterator)
         keys.push(key);
     assert_array_equals(keys, ['a', 'b', 'c'],
                         'The pairs to iterate over should be the return ' +
                         'value of an algorithm that implicitly makes a copy.');
 }, 'Iteration mutation');

[jsbell, 2016/12/12 16:54:50]

Can you add value mutations to this test?

 
+test(function(t) {
+    const headers = new Headers();
+    headers.append('b', '1');
+    headers.append('b', '2');
+    headers.append('a', '4');
+    headers.append('a', '2');
+    headers.append('a', '3');
+    const keys = [], values = [];
+    for (let [k, v] of headers){
+      keys.push(k);
+      values.push(v);
+    }
+    assert_array_equals(keys, ['a', 'b'],
+                        'The pairs to iterate over should be the return ' +
+                        'value of an algorithm that implicitly makes a copy.');
+    assert_array_equals(values, ['2,3,4', '1,2'],
+                        'The values should be sorted.');

[jsbell, 2016/12/12 16:54:50]

The spec does not indicate that values should be sorted. What is the behavior in
Firefox?

+},'Sorted and combined on iteration');

[jsbell, 2016/12/12 16:54:50]

nit: space after comma

+
 done();