PSA: Removing content::kAboutSrcDocURL - please use GURL::IsAboutSrcdoc() for comparisons

[Łukasz Anforowicz]

Hello //content embedders!

I just wanted to drop a note that https://crrev.com/c/1659195 removes content::kAboutSrcDocURL.  Going forward, please use |url.IsAboutSrcdoc()| instead of |url == GURL(content::kAboutSrcDocURL)| (similarily for about:blank - please use the IsAboutBlank method).  Unlike the constant-based / strict-equality comparisons, the GURL methods correctly account for things like about:blank#ref-tag.

Thanks,

Lukasz