Make block size a template parameter of SkTLList

Review URL: https://codereview.chromium.org/1457123002
diff --git a/src/gpu/GrReducedClip.h b/src/gpu/GrReducedClip.h
index a0ce08a..3a7c173 100644
--- a/src/gpu/GrReducedClip.h
+++ b/src/gpu/GrReducedClip.h
@@ -13,7 +13,7 @@
 
 class SK_API GrReducedClip {
 public:
-    typedef SkTLList<SkClipStack::Element> ElementList;
+    typedef SkTLList<SkClipStack::Element, 16> ElementList;
 
     enum InitialState {
         kAllIn_InitialState,