Never attempt to update the render tree on a dead document.

In https://src.chromium.org/viewvc/blink?revision=167137&view=revision
we added a check for change != Force before the check to
needsRenderTreeUpdate() update in updateRenderTree, but this means that
now if the change is Force you can skip the view() and isActive() checks
that are inside needsRenderTreeUpdate and then incorrectly attempt to
update the render tree of a dead document which will crash.

The ClusterFuzz test case in super hard to minimize, but this is clearly
what happens. This manifests as a crash in the release assert for
entering updateRenderTree from inside layout:

RELEASE_ASSERT(!view()->isInPerformLayout());

but what really happened is that view() is null.

BUG=377724

Review URL: https://codereview.chromium.org/415973003

git-svn-id: svn://svn.chromium.org/blink/trunk@178875 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Remove apparently unused ResourceFetcher::fetchUserCSSStyleSheet

A bit of clean up in preparation for teaching MemoryCache about
Service Workers. This removes a call to resourceForURL, which may need
to be complicated with an indication of the context of the request
like "requester is controlled by Service Worker X."

BUG=388375

Review URL: https://codereview.chromium.org/410303003

git-svn-id: svn://svn.chromium.org/blink/trunk@178876 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Move continuation outline painting logic into paintContinuationOutlines.

There is only one call site, in RenderBlock::paintObject. It has some
continuation outline painting logic at the call site; paintObject reads
more easily if this is moved inside.

BUG=302024

Review URL: https://codereview.chromium.org/410413009

git-svn-id: svn://svn.chromium.org/blink/trunk@178877 bbb929c8-8fbe-4397-9dbb-9b2b20218538