[6.0 and Chrome 77] Support Chrome 77 largestContentfulPaint (#906)
[6.0 and Chrome 77] Support Chrome 77 largestContentfulPaint (#906)

* Support Chrome 77 largestContentfulPaint

* copy the metrics

tobli/browsertime,sitespeedio/browsertime,sitespeedio/browsertime,sitespeedio/browsertime,sitespeedio/browsertime