WebKit is being picked up every day, I believe, sometimes even several times per day.Usually, the stable version has a WebKit revision from about a month and a half prior to the first stable version of a major version (so the WebKit version of 7 should be a snapshot of an early September WebKit).
To know for sure, go to http://omahaproxy.appspot.com/revision, type the full version number and you will get the Chrome revision number from which that major version was branched (this time it is 64615).
To get the WebKit revision, go to this URL -
(Replace "64615" with the revision number you got from the previous URL.)
And at the top of the file, there is this line -
"webkit_revision": "71013",
Which is the WebKit revision that was used for that release (71013).
Keep in mind that there might have been Chrome specific merges\reverts for WebKit after that version was branched, but if those changes were actually committed, they will usually be within the range of several, not a lot of changes.
You can also track those, if you are interested -
(Replace "517" with one of the full version numbers (7.0.517.44))