[CSS Exclusions] Improve ExclusionPolygon smart pointer safety
https://bugs.webkit.org/show_bug.cgi?id=114984

Reviewed by Dirk Schulze.

Assign newly allocated objects to PassOwnPtrs as early as possible to reduce the
chances of future leaks. No new tests were added, this change adds no new functionality.

* rendering/ExclusionPolygon.cpp:
(WebCore::computeShapePaddingBounds):
(WebCore::computeShapeMarginBounds):
(WebCore::ExclusionPolygon::shapePaddingBounds):
(WebCore::ExclusionPolygon::shapeMarginBounds):
* rendering/ExclusionShape.cpp:
(WebCore::ExclusionShape::createExclusionShape):


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@149003 268f45cc-cd09-0410-ab3c-d52691b4dbfc