public SkNVRefCnt<SnapshotArray>

Should fix broken build.

NOTRY=true
TBR=reed@google.com

BUG=skia:

Review URL: https://codereview.chromium.org/748143002
diff --git a/include/core/SkPicture.h b/include/core/SkPicture.h
index ea3db8e..d5c07a3 100644
--- a/include/core/SkPicture.h
+++ b/include/core/SkPicture.h
@@ -200,7 +200,7 @@
     bool hasText() const;
 
     // A refcounted array of refcounted const SkPicture pointers.
-    struct SnapshotArray : public SkNVRefCnt {
+    struct SnapshotArray : public SkNVRefCnt<SnapshotArray> {
         SnapshotArray(const SkPicture* pics[], size_t count) : fPics(pics), fCount(count) {}
         ~SnapshotArray() { for (size_t i = 0; i < fCount; i++) { fPics[i]->unref(); } }