SkTypes: use constexpr when appropriate

tests/CPlusPlusEleven.cpp

 /*
  * Copyright 2015 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 #include "Test.h"
 #include "SkTemplates.h"
 #include <utility>
 
@@ skipping 10 matching lines @@
 template <typename T> void deleter(T*) { }
 template <typename T> struct Deleter {
     void operator()(T* t) { delete static_cast<const Moveable*>(t); }
 };
 } // namespace
 
 DEF_TEST(CPlusPlusEleven_RvalueAndMove, r) {
     Moveable src1; Moveable dst1(std::move(src1));
     Moveable src2, dst2; dst2 = std::move(src2);
 }
+
+DEF_TEST(CPlusPlusEleven_constexpr, r) {
+    static constexpr int x = Sk32ToBool(50);
+    REPORTER_ASSERT(r, x == 1);
+    static constexpr int y = SkTPin<int>(100, 0, 10);
+    REPORTER_ASSERT(r, y == 10);
+}