Use stricter typing for traverse roots in SelectorQuery

Use stricter typing for traverse roots in SelectorQuery. We now use Element or
ContainerNode, as appropriate. This enables using the faster DOM traversal method
specializations as the compiler now knows these are container nodes and not
simply generic Node types.

R=esprehn, adamk

Review URL: https://codereview.chromium.org/153073002

git-svn-id: svn://svn.chromium.org/blink/trunk@166344 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Clarify what code handles 'An end tag whose tag name is "script"'

The "running a script" algorithm was renamed to "prepare a script" in
2011 <http://html5.org/r/5855>, but HTMLScriptRunner::runScript
doesn't actually correspond to that algorithm, so remove the comment.

BUG=none
NOTRY=true

Review URL: https://codereview.chromium.org/152903004

git-svn-id: svn://svn.chromium.org/blink/trunk@166345 bbb929c8-8fbe-4397-9dbb-9b2b20218538
user=kinuko
name=ws_waitable#a11684
email=kinuko@chromium.org
root=src/third_party/WebKit
issue=132913009
patchset=50001
bot=linux_blink,linux_blink_rel:


git-svn-id: svn://svn.chromium.org/blink/trunk@166346 bbb929c8-8fbe-4397-9dbb-9b2b20218538