Improve inPageCallback handling
Improve inPageCallback handling

This patch improves inPageCallback handling so that it doesn't
retain any variables.

brutalcrozt/puppeteer,michaelfward/puppeteer,brutalcrozt/puppeteer,GoogleChrome/puppeteer,ianchn/puppeteer,puppeteer/puppeteer,puppeteer/puppeteer,a1ph/puppeteer,michaelfward/puppeteer,GoogleChrome/puppeteer,elisherer/puppeteer,a1ph/puppeteer,GoogleChrome/puppeteer,puppeteer/puppeteer,puppeteer/puppeteer,ianchn/puppeteer,elisherer/puppeteer