feat: introduce puppeteer/Errors (#3056)

This patch adds a new require, `puppeteer/Errors`, that
holds all the Puppeteer-specific error classes.

Currently, the only custom error class we use is `TimeoutError`. We'll
expand in future with `CrashError` and some others.

Fixes #1694.

utils/doclint/check_public_api/index.js

@@ -22,6 +22,7 @@ const Message = require('../Message');
 const EXCLUDE_CLASSES = new Set([
   'CSSCoverage',
   'Connection',
+  'CustomError',
   'EmulationManager',
   'FrameManager',
   'JSCoverage',
@@ -35,11 +36,12 @@ const EXCLUDE_CLASSES = new Set([
   'WaitTask',
 ]);
 
-const EXCLUDE_METHODS = new Set([
+const EXCLUDE_PROPERTIES = new Set([
   'Browser.create',
   'Headers.fromPayload',
   'Page.create',
   'JSHandle.toString',
+  'TimeoutError.name',
 ]);
 
 /**
@@ -137,7 +139,7 @@ function filterJSDocumentation(jsDocumentation) {
       // Exclude all constructors by default.
       if (member.name === 'constructor' && member.type === 'method')
         return false;
-      return !EXCLUDE_METHODS.has(`${cls.name}.${member.name}`);
+      return !EXCLUDE_PROPERTIES.has(`${cls.name}.${member.name}`);
     });
     classes.push(new Documentation.Class(cls.name, members));
   }