Fix four memory leaks uncovered by valgrinding gm tests.

All are triggered by PDF code.
 Two are missing unref's on SkData.
 One is a missing unref on a SkAdvancedTypefaceMetrics.
 The last is missing destruction of SkClipStack internal state.

BUG=526

Review URL: https://codereview.appspot.com/5824049

git-svn-id: http://skia.googlecode.com/svn/trunk@3386 2bbb7eff-a529-9590-31e7-b0007b416f81
4 files changed