Add reminders that these classes have constexpr default constructors.

We can do this now that we can write "constexpr".

GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1936653002

Review-Url: https://codereview.chromium.org/1936653002

1 files changed, 2 insertions, 0 deletions

diff --git a/include/private/SkOnce.h b/include/private/SkOnce.h
index 1c68fb7da1..507dcb5b8c 100644
--- a/include/private/SkOnce.h
+++ b/include/private/SkOnce.h
@@ -19,6 +19,8 @@
 
 class SkOnce {
 public:
+    constexpr SkOnce() = default;
+
     template <typename Fn, typename... Args>
     void operator()(Fn&& fn, Args&&... args) {
         auto state = fState.load(std::memory_order_acquire);