feat(Console): Introduce ConsoleMessage type (#909)

This patch introduces ConsoleMessage type and starts dispatching
it for the 'console' event.

BREAKING CHANGE: this breaks the api of the 'console' event.

Fixes #744.

lib/Page.js

@@ -313,7 +313,9 @@ class Page extends EventEmitter {
       return;
     }
     const values = await Promise.all(event.args.map(arg => helper.serializeRemoteObject(this._client, arg)));
-    this.emit(Page.Events.Console, ...values);
+    const text = values.join(' ');
+    const message = new ConsoleMessage(event.type, text, values);
+    this.emit(Page.Events.Console, message);
   }
 
   _onDialog(event) {
@@ -875,6 +877,19 @@ Page.Viewport;
  * @property {("Strict"|"Lax")=} sameSite
  */
 
+class ConsoleMessage {
+  /**
+   * @param {string} type
+   * @param {string} text
+   * @param {!Array<*>} args
+   */
+  constructor(type, text, args) {
+    this.type = type;
+    this.text = text;
+    this.args = args;
+  }
+}
+
 
 module.exports = Page;
 helper.tracePublicAPI(Page);