Preserve custom headers when following cross-origin redirects.

third_party/WebKit/LayoutTests/http/tests/fetch/script-tests/thorough/redirect.js

 if (self.importScripts) {
   importScripts('/fetch/resources/fetch-test-helpers.js');
   importScripts('/fetch/resources/thorough-util.js');
 }
 
 var TEST_TARGETS = [
   // Redirect: same origin -> same origin
   [REDIRECT_URL + encodeURIComponent(BASE_URL) +
    '&mode=same-origin&method=GET',
    [fetchResolved, hasContentLength, hasServerHeader, hasBody, typeBasic],
@@ skipping 115 matching lines @@
    '&mode=cors&credentials=same-origin&method=POST&Status=307',
    [fetchResolved, noContentLength, noServerHeader, hasBody, typeCors],
    [methodIsPOST]],
   // The 308 redirect response MUST NOT change the method.
   // FIXME: disabled due to https://crbug.com/451938
   // [REDIRECT_URL + encodeURIComponent(OTHER_BASE_URL + '&ACAOrigin=*') +
   //  '&mode=cors&credentials=same-origin&method=POST&Status=308',
   //  [fetchResolved, noContentLength, noServerHeader, hasBody, typeCors],
   //  [methodIsPOST]],
 
+  // Custom header
+  [REDIRECT_URL +
+   encodeURIComponent(
+     OTHER_BASE_URL +
+     'ACAOrigin=*&ACAHeaders=x-serviceworker-test') +
+   '&mode=cors&credentials=same-origin&method=GET&headers=CUSTOM',
+   [fetchResolved, noContentLength, noServerHeader, hasBody, typeCors],
+   [methodIsGET, hasCustomHeader, authCheckNone]],
+  [REDIRECT_URL +
+   encodeURIComponent(
+     OTHER_BASE_URL +
+     'ACAOrigin=*') +
+   '&mode=cors&credentials=same-origin&method=GET&headers=CUSTOM',
+   [fetchRejected]],
+  [REDIRECT_URL +
+   encodeURIComponent(
+     OTHER_BASE_URL +
+     'ACAHeaders=x-serviceworker-test') +
+   '&mode=cors&credentials=same-origin&method=GET&headers=CUSTOM',
+   [fetchRejected]],
+
   // Server header
   [REDIRECT_URL +
    encodeURIComponent(
      OTHER_BASE_URL +
      '&ACAOrigin=' + BASE_ORIGIN +
      '&ACEHeaders=Content-Length, X-ServiceWorker-ServerHeader') +
    '&mode=cors&credentials=same-origin&method=GET',
    [fetchResolved, hasContentLength, hasServerHeader, hasBody, typeCors],
    [methodIsGET, authCheckNone]],
 
@@ skipping 140 matching lines @@
      'ACAOrigin=' + BASE_ORIGIN + '&ACAHeaders=x-serviceworker-test') +
    '&mode=cors&credentials=same-origin&method=GET&headers=CUSTOM' +
    '&ACAOrigin=' + BASE_ORIGIN + '&ACAHeaders=x-serviceworker-test',
    [fetchRejected]],
 ];
 
 if (self.importScripts) {
   executeTests(TEST_TARGETS);
   done();
 }