Reland of SkOncePtr -> SkOnce

src/ports/SkFontHost_mac.cpp

Index: src/ports/SkFontHost_mac.cpp
diff --git a/src/ports/SkFontHost_mac.cpp b/src/ports/SkFontHost_mac.cpp
index 72d4690870f4d54139b397055df95feb4f0a57d2..8593b396117ced96e3a4414b2d069fe03e849ecb 100644
--- a/src/ports/SkFontHost_mac.cpp
+++ b/src/ports/SkFontHost_mac.cpp
@@ -35,7 +35,7 @@
 #include "SkOTTable_hhea.h"
 #include "SkOTTable_loca.h"
 #include "SkOTUtils.h"
-#include "SkOncePtr.h"
+#include "SkOnce.h"
 #include "SkPaint.h"
 #include "SkPath.h"
 #include "SkSFNTHeader.h"
@@ -778,12 +778,12 @@
     return &legacy_CTFontDrawGlyphs;
 }
 
-SK_DECLARE_STATIC_ONCE_PTR(CTFontDrawGlyphsProc, gCTFontDrawGlyphs);
-
 CGRGBPixel* Offscreen::getCG(const SkScalerContext_Mac& context, const SkGlyph& glyph,
                              CGGlyph glyphID, size_t* rowBytesPtr,
                              bool generateA8FromLCD) {
-    auto ctFontDrawGlyphs = gCTFontDrawGlyphs.get(choose_CTFontDrawGlyphs);
+    static SkOnce once;
+    static CTFontDrawGlyphsProc* ctFontDrawGlyphs;
+    once([]{ ctFontDrawGlyphs = choose_CTFontDrawGlyphs(); });
 
     if (!fRGBSpace) {
         //It doesn't appear to matter what color space is specified.