SelectorChecker should not use CrossesBoundary behavior.

collectTreeBoundaryCrossingRules uses CrossesBoundary, but this causes
the following problem:

  <style>
    div#outer ^^ div#inner h1 { ...}
  </style>

div#inner h1 can cross treescope boundary.
Instead, we should use MatchRequest.applyAuthorStyles to skip treescope
check in ElementRuleCollector.

BUG=331871
TEST=fast/dom/shadow/style-with-cat.html

Review URL: https://codereview.chromium.org/113043005

git-svn-id: svn://svn.chromium.org/blink/trunk@164607 bbb929c8-8fbe-4397-9dbb-9b2b20218538