Document::didRemoveAllPendingStylesheet should consider hasNodesWithPlaceholderStyle()
    
While we have some pending stylesheet, StyleResolver::styleForElement returns s_styleNotYetAvailable style.
StyleResolver only checks whether there exist any pending stylesheets or not,
does not check what treeScope owns such pending styles.
    
So after the stylesheet is loaded, it is difficult to determine style recalc scope.
    
BUG=344729
TEST=fast/dom/shadow/import-rule-in-shadow-tree-needs-document-style-recalc.html

Review URL: https://codereview.chromium.org/171423006

git-svn-id: svn://svn.chromium.org/blink/trunk@167678 bbb929c8-8fbe-4397-9dbb-9b2b20218538