Enable ClangTidy check modernize-use-nullptr.

https://clang.llvm.org/extra/clang-tidy/checks/modernize-use-nullptr.html

The check converts the usage of null pointer constants (eg. NULL, 0) to
use the new C++11 nullptr keyword.

Change-Id: Iaea2d843154c70e49d62affdc5dceb3bca8c1089
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/310297
Commit-Queue: John Stiles <johnstiles@google.com>
Reviewed-by: Mike Klein <mtklein@google.com>
diff --git a/tests/InterpolatorTest.cpp b/tests/InterpolatorTest.cpp
index 813d2bf..b56a05b 100644
--- a/tests/InterpolatorTest.cpp
+++ b/tests/InterpolatorTest.cpp
@@ -21,7 +21,7 @@
     SkScalar        v1[3], v2[3], v[3];
     SkInterpolator::Result          result;
 
-    inter.setKeyFrame(0, 100, iset(v1, 10, 20, 30), 0);
+    inter.setKeyFrame(0, 100, iset(v1, 10, 20, 30), nullptr);
     inter.setKeyFrame(1, 200, iset(v2, 110, 220, 330));
 
     result = inter.timeToValues(0, v);