Put SkEmptyTypeface in anonymous namespace.

src/core/SkTypeface.cpp

Index: src/core/SkTypeface.cpp
diff --git a/src/core/SkTypeface.cpp b/src/core/SkTypeface.cpp
index 07b146736066b6a36e721829f4e99b13b502cf75..855ef909e8c4c17a53c60bb5b708086efbe94391 100644
--- a/src/core/SkTypeface.cpp
+++ b/src/core/SkTypeface.cpp
@@ -33,6 +33,8 @@ SkTypeface* (*gDeserializeTypefaceDelegate)(SkStream* ) = nullptr;
 
 ///////////////////////////////////////////////////////////////////////////////
 
+namespace {
+
 class SkEmptyTypeface : public SkTypeface {
 public:
     static SkEmptyTypeface* Create() { return new SkEmptyTypeface; }
@@ -74,6 +76,8 @@ protected:
     }
 };
 
+}
+
 SK_DECLARE_STATIC_MUTEX(gCreateDefaultMutex);
 SK_DECLARE_STATIC_ONCE_PTR(SkTypeface, defaults[4]);