Invert logic that prevented style sharing in findSharedStyle().
Invert logic that prevented style sharing in findSharedStyle().

https://src.chromium.org/viewvc/blink?view=rev&revision=159972 contained
a bug that prevented style sharing. This patch inverts the logic
so that if the parent supports style sharing, we do not return 0 from
SharedStyleFinder::findSharedStyle().

BUG=309935

Review URL: https://codereview.chromium.org/33183010

git-svn-id: bf5cd6ccde378db821296732a091cfbcf5285fbd@160172 bbb929c8-8fbe-4397-9dbb-9b2b20218538

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