chore(typescript): migrate src/Dialog (#5639)

This PR changes `src/Dialog.js` to `src/Dialog.ts` and rewrites
accordingly. Most of the changes are straight forward; the only
interesting one from a TS point of view is the `DialogType` enum. I
expose it again as `Dialog.Type` to avoid a breaking change.

This PR also exposed some bugs with our ESLint TypeScript settings and
applying the overrides, so I fixed those too.

I also updated our DocLint tool to work on TS source files over JS lib
files if they exist. This is the minimal change to keep the existing doc
system working as we're working on moving away from this system longer
term.

src/Dialog.ts

@@ -14,48 +14,46 @@
  * limitations under the License.
  */
 
-const {assert} = require('./helper');
+import helpers = require('./helper');
+
+const {assert} = helpers;
+
+enum DialogType {
+  Alert = 'alert',
+  BeforeUnload = 'beforeunload',
+  Confirm = 'confirm',
+  Prompt = 'prompt'
+}
 
 class Dialog {
-  /**
-   * @param {!Puppeteer.CDPSession} client
-   * @param {string} type
-   * @param {string} message
-   * @param {(string|undefined)} defaultValue
-   */
-  constructor(client, type, message, defaultValue = '') {
+  static Type = DialogType;
+
+  private _client: Puppeteer.CDPSession;
+  private _type: DialogType;
+  private _message: string;
+  private _defaultValue: string;
+  private _handled = false;
+
+  constructor(client: Puppeteer.CDPSession, type: DialogType, message: string, defaultValue = '') {
     this._client = client;
     this._type = type;
     this._message = message;
-    this._handled = false;
     this._defaultValue = defaultValue;
   }
 
-  /**
-   * @return {string}
-   */
-  type() {
+  type(): DialogType {
     return this._type;
   }
 
-  /**
-   * @return {string}
-   */
-  message() {
+  message(): string {
     return this._message;
   }
 
-  /**
-   * @return {string}
-   */
-  defaultValue() {
+  defaultValue(): string {
     return this._defaultValue;
   }
 
-  /**
-   * @param {string=} promptText
-   */
-  async accept(promptText) {
+  async accept(promptText?: string): Promise<void> {
     assert(!this._handled, 'Cannot accept dialog which is already handled!');
     this._handled = true;
     await this._client.send('Page.handleJavaScriptDialog', {
@@ -64,7 +62,7 @@ class Dialog {
     });
   }
 
-  async dismiss() {
+  async dismiss(): Promise<void> {
     assert(!this._handled, 'Cannot dismiss dialog which is already handled!');
     this._handled = true;
     await this._client.send('Page.handleJavaScriptDialog', {
@@ -73,11 +71,4 @@ class Dialog {
   }
 }
 
-Dialog.Type = {
-  Alert: 'alert',
-  BeforeUnload: 'beforeunload',
-  Confirm: 'confirm',
-  Prompt: 'prompt'
-};
-
-module.exports = {Dialog};
+export = {Dialog};