Speculative fix for preloader crash in synchronous HTML parsing
Speculative fix for preloader crash in synchronous HTML parsing

The |m_preloader| should always be available for synchronous parsing via
document.write(), however, it seems not be the case.
This CL adds an ASSERT to catch it, and workaround if statement so that
it would just skip preloading instead of crash if the condition doesn't hold.

BUG=465478

Review URL: https://codereview.chromium.org/997803004

git-svn-id: bf5cd6ccde378db821296732a091cfbcf5285fbd@192604 bbb929c8-8fbe-4397-9dbb-9b2b20218538

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