DevTools: [Elements] Display invisible characters as HTML entities in attribute values

R=aandrey, eustas, vsevik
BUG=330388

Review URL: https://codereview.chromium.org/105663006

git-svn-id: svn://svn.chromium.org/blink/trunk@164312 bbb929c8-8fbe-4397-9dbb-9b2b20218538