add AnalysisContext scanHtml

Review URL: https://codereview.chromium.org//12314089

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge@18951 260f80e4-7a28-3924-810f-c04153c831b5
cleanup AnalysisContext scanHtml

Review URL: https://codereview.chromium.org//12320085

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge@18952 260f80e4-7a28-3924-810f-c04153c831b5
add HTML token type

Review URL: https://codereview.chromium.org//12310093

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge@18953 260f80e4-7a28-3924-810f-c04153c831b5