Don't allow nullptr in texels array params (unless using a transfer buffer).

include/gpu/GrTextureProvider.h

Index: include/gpu/GrTextureProvider.h
diff --git a/include/gpu/GrTextureProvider.h b/include/gpu/GrTextureProvider.h
index 83efb5bf7b0622c3568a4f3d3e0b69e972606c5f..7c12ebd6db36152535185c8e15d05d7839e937be 100644
--- a/include/gpu/GrTextureProvider.h
+++ b/include/gpu/GrTextureProvider.h
@@ -45,7 +45,7 @@ public:
 
     /** Shortcut for creating a texture with no initial data to upload. */
     GrTexture* createTexture(const GrSurfaceDesc& desc, SkBudgeted budgeted) {
-        return this->createTexture(desc, budgeted, NULL, 0);
+        return this->createTexture(desc, budgeted, nullptr, 0);
     }
 
     /** Assigns a unique key to the texture. The texture will be findable via this key using