Replace a lot of 'static const' with 'constexpr' or 'const'.

gm/lighting.cpp

Index: gm/lighting.cpp
diff --git a/gm/lighting.cpp b/gm/lighting.cpp
index 7915c331d0d03edf4da18876a35093d97bb113f6..cd4132e1b560b96c7dcdeeb2ee8aaefb0fa7ed84 100644
--- a/gm/lighting.cpp
+++ b/gm/lighting.cpp
@@ -158,14 +158,14 @@ protected:
     }
 
     bool onAnimate(const SkAnimTimer& timer) override {
-        static const SkScalar kDesiredDurationSecs = 15.0f;
+        constexpr SkScalar kDesiredDurationSecs = 15.0f;
 
         fAzimuth = kStartAzimuth + timer.scaled(360.0f/kDesiredDurationSecs, 360.0f);
         return true;
     }
 
 private:
-    static const int kStartAzimuth = 225;
+    static constexpr int kStartAzimuth = 225;
 
     SkBitmap fBitmap;
     SkScalar fAzimuth;