Disallow access to opaque CSS responses.

Bug: 848786
Change-Id: Ie53fbf644afdd76d7c65649a05c939c63d89b4ec
Reviewed-on: https://chromium-review.googlesource.com/1088335
Reviewed-by: Kouhei Ueno <kouhei@chromium.org>
Commit-Queue: Matt Falkenhagen <falken@chromium.org>
Cr-Commit-Position: refs/heads/master@{#565537}
  StyleSheetCSSRuleList(CSSStyleSheet* sheet) : style_sheet_(sheet) {}

  StyleSheetCSSRuleList(CSSStyleSheet* sheet) : style_sheet_(sheet) {}
