You can get an approximation using the Webkit version tag as it appears in the User-Agent:
Take, for example, the following user agent:
Mozilla / 5.0 (Macintosh; Intel Mac OS X 10_6_8) AppleWebKit / 537.13 + (KHTML, e.g. Gecko) Version /5.1.7 Safari / 534.57.2
The version of Webkit is advertised here as 537.13+ . This version tag is created from the following source file:
https://trac.webkit.org/browser/trunk/Source/WebCore/Configurations/Version.xcconfig
You can then see which versions of SVN embed this specification tag.
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