Trace more methods under HTMLDocumentParser::insert

This should help us better understand long
HTMLDocumentParser::insert blocks when we encounter
them on traces.

BUG=356292

Review URL: https://codereview.chromium.org/208793004

git-svn-id: svn://svn.chromium.org/blink/trunk@170464 bbb929c8-8fbe-4397-9dbb-9b2b20218538