Add plumbing in blink to allow overriding the skia font manager.

skia/config/sk_ref_cnt_ext_debug.h

Index: skia/config/sk_ref_cnt_ext_debug.h
diff --git a/skia/config/sk_ref_cnt_ext_debug.h b/skia/config/sk_ref_cnt_ext_debug.h
index 78a39a3789f23cb5cbc2a9f23c74a60ec4a5c5ae..8a4e448a3d13016ad1b2bbe942519368dacc138a 100644
--- a/skia/config/sk_ref_cnt_ext_debug.h
+++ b/skia/config/sk_ref_cnt_ext_debug.h
@@ -11,16 +11,23 @@
 
 #include <atomic>
 
+class SkRefCnt;
+
+namespace WTF {
+  void adopted(const SkRefCnt*);
+  void requireAdoption(const SkRefCnt*);
+}
+
 // Alternate implementation of SkRefCnt for Chromium debug builds
 class SK_API SkRefCnt : public SkRefCntBase {
 public:
   SkRefCnt();
   ~SkRefCnt() override;
   void ref() const { SkASSERT(flags_.load() != AdoptionRequired_Flag); SkRefCntBase::ref(); }
-  void adopted() const { flags_ |= Adopted_Flag; }
-  void requireAdoption() const { flags_ |= AdoptionRequired_Flag; }
   void deref() const { SkRefCntBase::unref(); }
 private:
+  void adopted() const { flags_ |= Adopted_Flag; }
+  void requireAdoption() const { flags_ |= AdoptionRequired_Flag; }
 
   enum {
     Adopted_Flag = 0x1,
@@ -28,6 +35,9 @@ private:
   };
 
   mutable std::atomic<int> flags_;
+
+  friend void WTF::adopted(const SkRefCnt*);
+  friend void WTF::requireAdoption(const SkRefCnt*);
 };
 
 inline SkRefCnt::SkRefCnt() : flags_(0) { }