Remove RequireCSSExtensionForFile runtime enabled flag.

The feature has long since been stable (since M64) and doesn't seem
to be a need for this flag.

BUG=788936

Change-Id: I666390b869289c328acb4a2daa5bf4154e1702c0
Reviewed-on: https://chromium-review.googlesource.com/c/1324143
Reviewed-by: Mike West <mkwst@chromium.org>
Reviewed-by: Camille Lamy <clamy@chromium.org>
Commit-Queue: Dave Tapuska <dtapuska@chromium.org>
Cr-Commit-Position: refs/heads/master@{#607329}
void CSSStyleSheetResource::DestroyDecodedDataIfPossible() {
  if (!parsed_style_sheet_cache_)
    return;

  SetParsedStyleSheetCache(nullptr);
}

void CSSStyleSheetResource::DestroyDecodedDataIfPossible() {
  if (!parsed_style_sheet_cache_)
    return;

  SetParsedStyleSheetCache(nullptr);
}
