DevTools: add more logging to console-viewport-selection.html

The patch adds more logging to the console-viewport-selection.html test
to figure out possible source of its flakiness.

BUG=390204
TBR=vsevik

Review URL: https://codereview.chromium.org/392643002

git-svn-id: svn://svn.chromium.org/blink/trunk@178070 bbb929c8-8fbe-4397-9dbb-9b2b20218538