fix(network): be able to remove headers using request.continue (#4797)

I think this was a regression caused here https://github.com/GoogleChrome/puppeteer/pull/4265/files#diff-d2ac7cb061b0c51644d0a5d6140e3a32R446

Fix #4743

experimental/puppeteer-firefox/lib/NetworkManager.js

@@ -158,7 +158,7 @@ class Request {
     } = overrides;
     await this._session.send('Network.resumeSuspendedRequest', {
       requestId: this._id,
-      headers: headers ? Object.entries(headers).map(([name, value]) => ({name, value})) : undefined,
+      headers: headers ? Object.entries(headers).filter(([, value]) => !Object.is(value, undefined)).map(([name, value]) => ({name, value})) : undefined,
     }).catch(error => {
       debugError(error);
     });

lib/NetworkManager.js

@@ -723,8 +723,10 @@ class SecurityDetails {
  */
 function headersArray(headers) {
   const result = [];
-  for (const name in headers)
-    result.push({name, value: headers[name] + ''});
+  for (const name in headers) {
+    if (!Object.is(headers[name], undefined))
+      result.push({name, value: headers[name] + ''});
+  }
   return result;
 }
 

test/requestinterception.spec.js

@@ -72,6 +72,24 @@ module.exports.addTests = function({testRunner, expect, CHROME}) {
       });
       await page.goto(server.PREFIX + '/rrredirect');
     });
+    // @see https://github.com/GoogleChrome/puppeteer/issues/4743
+    it('should be able to remove headers', async({page, server}) => {
+      await page.setRequestInterception(true);
+      page.on('request', request => {
+        const headers = Object.assign({}, request.headers(), {
+          foo: 'bar',
+          origin: undefined, // remove "origin" header
+        });
+        request.continue({ headers });
+      });
+
+      const [serverRequest] = await Promise.all([
+        server.waitForRequest('/empty.html'),
+        page.goto(server.PREFIX + '/empty.html')
+      ]);
+
+      expect(serverRequest.headers.origin).toBe(undefined);
+    });
     it('should contain referer header', async({page, server}) => {
       await page.setRequestInterception(true);
       const requests = [];