RenderView is null for import documents.

RenderView is null for import documents.

Documents for html imports have separate StyleEngines and separate lists of
pending stylesheets. However, they don't have a RenderView. In r176050 the
repaint was moved from the StyleEngine where non-master documents skipped
the repaint. Trying to do a repaint from a non-master document will crash
without a check for renderView().

I have added a renderView() check with an assert that checks that it happens
if we are in an import document. I did keep the changing of
m_pendingSheetLayout to IgnoreLayoutWithPendingSheets, since we
envidentially do set it to DidLayoutWithPendingSheets for import documents,
even before the r176050 change.

It is possible that the m_pendingSheetLayout machinery does nothing useful
for imported documents, but I frankly don't know how it should work.

I am only able to reproduce the crash in the layout test with --debug.

R=ojan@chromium.org,esprehn@chromium.org
BUG=386564
Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=176649

[rune, 2014-06-20 12:14:51]

PTAL

[rune, 2014-06-20 18:17:14]

I'll be able to fix issues in this CL during the weekend, but on vacation for a
week from Monday.

[esprehn, 2014-06-20 18:21:05]

lgtm

[commit-bot: I haz the power, 2014-06-20 18:22:21]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/rune@opera.com/330093003/1

[commit-bot: I haz the power, 2014-06-20 21:44:29]

Change committed as 176649