Add delay option to input methods (#171)

Add delay option to input methods for the keyboard and mouse.

Closes #156

lib/Page.js

@@ -532,12 +532,19 @@ class Page extends EventEmitter {
 
   /**
    * @param {string} text
+   * @param {{delay: (number|undefined)}=} options
    * @return {!Promise}
    */
-  async type(text) {
+  async type(text, options) {
+    let delay = 0;
+    if (options && options.delay)
+      delay = options.delay;
     let last;
-    for (let char of text)
-      last = this.press(char, {text: char});
+    for (let char of text) {
+      last = this.press(char, {text: char, delay});
+      if (delay)
+        await new Promise(f => setTimeout(f, delay));
+    }
     await last;
   }
 
@@ -548,6 +555,8 @@ class Page extends EventEmitter {
    */
   async press(key, options) {
     this._keyboard.down(key, options);
+    if (options && options.delay)
+      await new Promise(f => setTimeout(f, options.delay));
     await this._keyboard.up(key);
   }