Should remove StyleSheetContents from cache even if document is not active.

StyleSheetContents cache works independent of document's active(),
because StyleElement::process() always invokes StyleEngine::createSheet().

So removeSheetFromCache should also remove 'this' from the cache independent of document's active().

BUG=353894
TEST=fast/dom/move-style-element-to-inactive-document-crash.html

Review URL: https://codereview.chromium.org/204423002

git-svn-id: svn://svn.chromium.org/blink/trunk@169595 bbb929c8-8fbe-4397-9dbb-9b2b20218538