View-source fails to display < in opening tag near chunk boundaries.

If current buffer is terminated with '....<', the token remains in the state Uninitialized and after next ::start call when a new chunk will be received, HTMLSourceTracker cleans previous buffer with '<' symbol. And view-source will contain something like: ... <b></b>b></b> ...

BUG=168581

Review URL: https://codereview.chromium.org/351353005

git-svn-id: svn://svn.chromium.org/blink/trunk@177331 bbb929c8-8fbe-4397-9dbb-9b2b20218538