Enable ASSERT(attribute.nameRange.start) in AtomicHTMLToken::initializeAttributes

Restore it since the referred bug is already in the trunk.

BUG=

Review URL: https://codereview.chromium.org/345733003

git-svn-id: svn://svn.chromium.org/blink/trunk@176528 bbb929c8-8fbe-4397-9dbb-9b2b20218538