[PDF] Clean up ref counting.

Return ref'd objs where possible enabling removal of many SkRefPtr<> variables.

Review URL: http://codereview.appspot.com/4029051

git-svn-id: http://skia.googlecode.com/svn/trunk@750 2bbb7eff-a529-9590-31e7-b0007b416f81
15 files changed