chore(types): generate a d.ts file for protocol types (#2325)

This uses the `/json/protocol` endpoint to generate type definitions for the protocol.

Currently it is lacking protocol events and commands, but I will add those later.

lib/ExecutionContext.js

@@ -19,7 +19,7 @@ const {helper} = require('./helper');
 class ExecutionContext {
   /**
    * @param {!Puppeteer.CDPSession} client
-   * @param {!Object} contextPayload
+   * @param {!Protocol.Runtime.ExecutionContextDescription} contextPayload
    * @param {function(*):!JSHandle} objectHandleFactory
    * @param {?Puppeteer.Frame} frame
    */
@@ -127,7 +127,7 @@ class JSHandle {
   /**
    * @param {!ExecutionContext} context
    * @param {!Puppeteer.CDPSession} client
-   * @param {!Object} remoteObject
+   * @param {!Protocol.Runtime.RemoteObject} remoteObject
    */
   constructor(context, client, remoteObject) {
     this._context = context;