feat(page): add an option to disable timeout for waitForFunction (#2252)

This patch adds support for `timeout: 0` to disable timeout for the following functions:
- `page.waitForFunction`
- `page.waitForXPath`
- `page.waitForSelector`
and their `frame` counterparts.

Fixes #2200

lib/FrameManager.js

@@ -790,7 +790,8 @@ class WaitTask {
     });
     // Since page navigation requires us to re-install the pageScript, we should track
     // timeout on our end.
-    this._timeoutTimer = setTimeout(() => this.terminate(new Error(`waiting failed: timeout ${timeout}ms exceeded`)), timeout);
+    if (timeout)
+      this._timeoutTimer = setTimeout(() => this.terminate(new Error(`waiting failed: timeout ${timeout}ms exceeded`)), timeout);
     this.rerun();
   }