Cleanups for VTTTokenizer

Get rid of VTTTokenizer::m_token, and hence remove the need to play
games with pointers to the resulting token, since the token is now
produced at the end of VTTTokenizer::nextToken. This renders the reset()
method empty (and it wasn't previously used outside of VTTTokenizer), so
remove it.

Make a local, tailored, version of the ADVANCE_TO macro to get rid of the
redundant check of advance(). This in turn allows removing the (now
useless) part of the scaffolding which is haveBufferedCharacterToken(),
as well as turning VTTTokenizer::m_state into the local 'state' and
moving the definition of the state enumeration into the cpp-file.
This also means the state defintions can be moved from the header-file,
so do that as well.

BUG=319391

Review URL: https://codereview.chromium.org/98763004

git-svn-id: svn://svn.chromium.org/blink/trunk@162994 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Remove TreatNullAs=NullString for HTMLKeygenElement

http://whatwg.org/html#htmlkeygenelement

The tests for the updated properties pass in Firefox Nightly, IE11
Release Preview and Opera 12.16, with these exceptions:

Firefox and IE support none of the attributes and thus fail all tests.

Opera reflects keytype as the empty string.

BUG=310298

Review URL: https://codereview.chromium.org/98543003

git-svn-id: svn://svn.chromium.org/blink/trunk@162995 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Remove TreatNullAs=NullString for HTMLLinkElement

http://whatwg.org/html#htmllinkelement
http://whatwg.org/html#HTMLLinkElement-partial

The tests for the updated properties pass in Firefox Nightly, IE11
Release Preview and Opera 12.16.

BUG=310298

Review URL: https://codereview.chromium.org/98313003

git-svn-id: svn://svn.chromium.org/blink/trunk@162996 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Remove TreatNullAs=NullString for HTMLModElement

http://whatwg.org/html#htmlmodelement

The tests for the updated properties pass in Firefox Nightly, IE11
Release Preview and Opera 12.16.

BUG=310298

Review URL: https://codereview.chromium.org/99213002

git-svn-id: svn://svn.chromium.org/blink/trunk@162997 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Remove duplicated headers from wtf/ directory where the implementation file includes the same dependencies as the corresponding primary header.

BUG=317231

Review URL: https://codereview.chromium.org/98183002

git-svn-id: svn://svn.chromium.org/blink/trunk@162998 bbb929c8-8fbe-4397-9dbb-9b2b20218538