Unify ThreadID.

include/private/SkThreadID.h

Index: include/private/SkThreadID.h
diff --git a/src/ports/SkFontMgr_fontconfig_factory.cpp b/include/private/SkThreadID.h
similarity index 53%
copy from src/ports/SkFontMgr_fontconfig_factory.cpp
copy to include/private/SkThreadID.h
index cdf055608d5477d2e4762dae1dbeacef6490850b..5f3504fab391d06c4ac0d67c035230a235986d93 100644
--- a/src/ports/SkFontMgr_fontconfig_factory.cpp
+++ b/include/private/SkThreadID.h
@@ -5,10 +5,13 @@
  * found in the LICENSE file.
  */
 
-#include "SkFontMgr.h"
-#include "SkFontMgr_fontconfig.h"
+#ifndef SkThreadID_DEFINED
+#define SkThreadID_DEFINED
+
 #include "SkTypes.h"
 
-SkFontMgr* SkFontMgr::Factory() {
-    return SkFontMgr_New_FontConfig(nullptr);
-}
+typedef int64_t SkThreadID;
+
+SkThreadID SkGetThreadID();
+
+#endif  // SkThreadID_DEFINED