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

gm/lightingshader.cpp

Index: gm/lightingshader.cpp
diff --git a/gm/lightingshader.cpp b/gm/lightingshader.cpp
index 137fd64a26caf68cd3176e8b52fc531e48a32863..8576dd72d57a1d4debd8480549ab72728ac8f1d6 100644
--- a/gm/lightingshader.cpp
+++ b/gm/lightingshader.cpp
@@ -66,7 +66,7 @@ protected:
         kLast_NormalMap = kTetra_NormalMap
     };
 
-    static const int kNormalMapCount = kLast_NormalMap+1;
+    static constexpr int kNormalMapCount = kLast_NormalMap+1;
 
     SkString onShortName() override {
         return SkString("lightingshader");
@@ -164,8 +164,8 @@ protected:
     }
 
 private:
-    static const int kTexSize = 128;
-    static const int kGMSize  = 512;
+    static constexpr int kTexSize = 128;
+    static constexpr int kGMSize  = 512;
 
     SkBitmap        fDiffuse;
     SkBitmap        fNormalMaps[kNormalMapCount];