SVGPropertyTearOffs should detachChildren before deleting its value.
SVGPropertyTearOffs should detachChildren before deleting its value.

TEST=svg/transforms/svg-matrix-tearoff-crash.html
BUG=296276

Review URL: https://codereview.chromium.org/25314003

git-svn-id: bf5cd6ccde378db821296732a091cfbcf5285fbd@158563 bbb929c8-8fbe-4397-9dbb-9b2b20218538

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