puppeteer: allow disabling default viewport

null disables the default viewport (verified locally). comment already mentions that, but it wasn't accepted in the type.

types/puppeteer/index.d.ts

@@ -2044,7 +2044,7 @@ export interface BrowserOptions {
      * @default false
      */
     isLandscape?: boolean;
-  };
+  } | null;
   /**
    * Slows down Puppeteer operations by the specified amount of milliseconds.
    * Useful so that you can see what is going on.

types/puppeteer/puppeteer-tests.ts

@@ -200,6 +200,13 @@ puppeteer.launch().then(async browser => {
   browser.close();
 })();
 
+// Launching with default viewport disabled
+(async () => {
+  await puppeteer.launch({
+    defaultViewport: null
+  });
+})();
+
 // Test v0.12 features
 (async () => {
   const browser = await puppeteer.launch({