Unroll isDocumentElement in BlockPainter to isolate a crash
Unroll isDocumentElement in BlockPainter to isolate a crash

The crash covered by the bug is enduring and local, but rare and
largely impossible to reproduce. Some memory somewhere does not
contain what it should. In an effort to identify which value is bad,
this patch unrolls the isDocumentElement method such that each line
uses only one object's data.

The TODO reminds us to remove this once we track down the problem.

R=chrishtr@chromium.org
BUG=475698

Review URL: https://codereview.chromium.org/1102963003

git-svn-id: bf5cd6ccde378db821296732a091cfbcf5285fbd@194628 bbb929c8-8fbe-4397-9dbb-9b2b20218538

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