Reland of SkOncePtr -> SkOnce (patchset #1 id:1 of https://codereview.chromium.org/1945293004/ )

Reason for revert:
previous revert unneeded (I think)

Original issue's description:
> Revert of SkOncePtr -> SkOnce (patchset #4 id:60001 of https://codereview.chromium.org/1953533002/ )
>
> Reason for revert:
> broken the Mac and Linux builders, e.g.:
>
> https://build.chromium.org/p/chromium/builders/Mac/builds/15151
> https://build.chromium.org/p/chromium/builders/Linux%20x64/builds/19052
>
> Original issue's description:
> > SkOncePtr -> SkOnce
> >
> > It's always nice to kill off a synchronization primitive.
> > And while less terse, I think this new code reads more clearly.
> >
> > ... and, SkOncePtr's tests were the only thing now using sk_num_cores()
> > outside of SkTaskGroup, so I've hidden it as static inside SkTaskGroup.cpp.
> >
> > BUG=skia:
> > GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1953533002
> > CQ_EXTRA_TRYBOTS=client.skia:Test-Ubuntu-GCC-GCE-CPU-AVX2-x86_64-Release-SKNX_NO_SIMD-Trybot
> >
> > Committed: https://skia.googlesource.com/skia/+/9bd3fc7fa9bb7cad050bd619aa93d4c48ebb5c02
>
> TBR=herb@google.com,mtklein@chromium.org
> # Skipping CQ checks because original CL landed less than 1 days ago.
> NOPRESUBMIT=true
> NOTREECHECKS=true
> NOTRY=true
> BUG=skia:
>
> Committed: https://skia.googlesource.com/skia/+/7eb33da7eede34c050b865dbb1b60c3dcea7191b

TBR=herb@google.com,mtklein@chromium.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=skia:

Review-Url: https://codereview.chromium.org/1949313003

1 files changed, 6 insertions, 4 deletions

diff --git a/src/utils/SkEventTracer.cpp b/src/utils/SkEventTracer.cpp
index 32a0207c23..0a748d1464 100644
--- a/src/utils/SkEventTracer.cpp
+++ b/src/utils/SkEventTracer.cpp
@@ -7,7 +7,7 @@
 
 #include "SkAtomics.h"
 #include "SkEventTracer.h"
-#include "SkOncePtr.h"
+#include "SkOnce.h"
 
 #include <stdlib.h>
 
@@ -39,9 +39,8 @@ class SkDefaultEventTracer : public SkEventTracer {
     }
 };
 
-// We prefer gUserTracer if it's been set, otherwise we fall back on gDefaultTracer.
+// We prefer gUserTracer if it's been set, otherwise we fall back on a default tracer;
 static SkEventTracer* gUserTracer = nullptr;
-SK_DECLARE_STATIC_ONCE_PTR(SkDefaultEventTracer, gDefaultTracer);
 
 void SkEventTracer::SetInstance(SkEventTracer* tracer) {
     SkASSERT(nullptr == sk_atomic_load(&gUserTracer, sk_memory_order_acquire));
@@ -54,5 +53,8 @@ SkEventTracer* SkEventTracer::GetInstance() {
     if (SkEventTracer* tracer = sk_atomic_load(&gUserTracer, sk_memory_order_acquire)) {
         return tracer;
     }
-    return gDefaultTracer.get([]{ return new SkDefaultEventTracer; });
+    static SkOnce once;
+    static SkDefaultEventTracer* defaultTracer;
+    once([] { defaultTracer = new SkDefaultEventTracer; });
+    return defaultTracer;
 }