Mark overridden destructors with 'override' and remove 'virtual'

This silences a new warning in clang 5.0

Change-Id: Ieb5b75a6ffed60107c3fd16075d2ecfd515b55e8
Reviewed-on: https://skia-review.googlesource.com/10006
Commit-Queue: Brian Salomon <bsalomon@google.com>
Reviewed-by: Mike Klein <mtklein@chromium.org>
diff --git a/src/core/SkPictureRecord.h b/src/core/SkPictureRecord.h
index 4e0bf46..dc9a002 100644
--- a/src/core/SkPictureRecord.h
+++ b/src/core/SkPictureRecord.h
@@ -30,7 +30,7 @@
 class SkPictureRecord : public SkCanvas {
 public:
     SkPictureRecord(const SkISize& dimensions, uint32_t recordFlags);
-    virtual ~SkPictureRecord();
+    ~SkPictureRecord() override;
 
     const SkTDArray<const SkPicture* >& getPictureRefs() const {
         return fPictureRefs;