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
diff --git a/include/core/SkClipStack.h b/include/core/SkClipStack.h
index fc96f03..306ba2a 100644
--- a/include/core/SkClipStack.h
+++ b/include/core/SkClipStack.h
@@ -18,7 +18,7 @@
 public:
     SkClipStack();
     SkClipStack(const SkClipStack& b);
-    ~SkClipStack() {}
+    ~SkClipStack();
 
     SkClipStack& operator=(const SkClipStack& b);
     bool operator==(const SkClipStack& b) const;