PageRuleCollector constructor should take rootElementStyle directly.

Since PageRuleCollector uses only rootElementStyle() of ElementResolveContext and ElementResolveContext might have no rootElementStyle (document has no documentElement),
PageRuleCollector constructor should directly take rootElementStyle and initialize its memeber variables.

BUG=288103
TEST=printing/print-document-without-documentElement-crash.html covers.

Review URL: https://codereview.chromium.org/23876014

git-svn-id: svn://svn.chromium.org/blink/trunk@159415 bbb929c8-8fbe-4397-9dbb-9b2b20218538