[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..10af63cfa9c84e06b8aa0a0e0f46f608f334e6c8 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
@@ -239,6 +239,8 @@ test(function(t) {
     headers.set('a', '1');
     headers.set('b', '2');
     headers.set('c', '3');
+    headers.append('a', '2');
+    headers.append('a', '3');
 
     const iterator = headers.entries();
 
@@ -246,11 +248,16 @@ test(function(t) {
     headers.set('d', '4');
 
     const keys = [];
-    for (let [key, value] of iterator)
+    const values = [];
+    for (let [key, value] of iterator){

[jsbell, 2016/12/12 22:38:31]

nit: space between ) and {

         keys.push(key);
+        values.push(value);
+      }

[jsbell, 2016/12/12 22:38:31]

nit: } should line up with for

     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.');
+    assert_array_equals(values, ['1,2,3', '2', '3'],
+                        "The values should be combined and separated by ','.");
 }, 'Iteration mutation');
 
 done();