Reland of SkOncePtr -> SkOnce

src/core/SkMessageBus.h

Index: src/core/SkMessageBus.h
diff --git a/src/core/SkMessageBus.h b/src/core/SkMessageBus.h
index a2802f06d40141f34951c0b16b253d04cb54b094..79f5c026dcde2ee82e9ffc5f74007e54f55dfe14 100644
--- a/src/core/SkMessageBus.h
+++ b/src/core/SkMessageBus.h
@@ -9,7 +9,7 @@
 #define SkMessageBus_DEFINED
 
 #include "SkMutex.h"
-#include "SkOncePtr.h"
+#include "SkOnce.h"
 #include "SkTArray.h"
 #include "SkTDArray.h"
 #include "SkTypes.h"
@@ -47,10 +47,12 @@
 // This must go in a single .cpp file, not some .h, or we risk creating more than one global
 // SkMessageBus per type when using shared libraries.  NOTE: at most one per file will compile.
 #define DECLARE_SKMESSAGEBUS_MESSAGE(Message)                      \
-    SK_DECLARE_STATIC_ONCE_PTR(SkMessageBus<Message>, bus);        \
     template <>                                                    \
     SkMessageBus<Message>* SkMessageBus<Message>::Get() {          \
-        return bus.get([]{ return new SkMessageBus<Message>(); }); \
+        static SkOnce once;                                        \
+        static SkMessageBus<Message>* bus;                         \
+        once([] { bus = new SkMessageBus<Message>(); });           \
+        return bus;                                                \
     }
 
 //   ----------------------- Implementation of SkMessageBus::Inbox -----------------------