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

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

Index: third_party/WebKit/LayoutTests/http/tests/fetch/script-tests/headers.js
diff --git a/third_party/WebKit/LayoutTests/http/tests/fetch/script-tests/headers.js b/third_party/WebKit/LayoutTests/http/tests/fetch/script-tests/headers.js
index a87a75febb4649089b93afcb12235d1a2b5a4113..f42bc0dfebab4bc95197a51a8d2da7f05ef246d4 100644
--- a/third_party/WebKit/LayoutTests/http/tests/fetch/script-tests/headers.js
+++ b/third_party/WebKit/LayoutTests/http/tests/fetch/script-tests/headers.js
@@ -253,4 +253,23 @@ test(function(t) {
                         '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();