Histogram fix: WebCore.Scripts.ParsingBlocking.TimeBetweenLoadedAndCompiled; exclude internal resources.

Some chrome:// scripts are compiled several times after loading; exclude them
from the data. Internal scripts (or scripts loaded via file://) are not interesting
from this histogram's point of view anyway and unnecessarily skew the data.

BUG=

Review URL: https://codereview.chromium.org/572883002

git-svn-id: svn://svn.chromium.org/blink/trunk@182047 bbb929c8-8fbe-4397-9dbb-9b2b20218538