move SkBlendMode_Name into public (for chrome)

BUG=skia:

GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=4905

Change-Id: I4f6cbc7b4d2a9d41ba5da39d550961587f30a4ac
Reviewed-on: https://skia-review.googlesource.com/4905
Reviewed-by: Mike Reed <reed@google.com>
Commit-Queue: Mike Reed <reed@google.com>
diff --git a/include/core/SkBlendMode.h b/include/core/SkBlendMode.h
index eb3469f..3f8f30c 100644
--- a/include/core/SkBlendMode.h
+++ b/include/core/SkBlendMode.h
@@ -8,6 +8,8 @@
 #ifndef SkBlendMode_DEFINED
 #define SkBlendMode_DEFINED
 
+#include "SkTypes.h"
+
 enum class SkBlendMode {
     kClear,    //!< [0, 0]
     kSrc,      //!< [Sa, Sc]
@@ -48,4 +50,9 @@
     kLastMode = kLuminosity
 };
 
+/**
+ *  Return the (c-string) name of the blendmode.
+ */
+SK_API const char* SkBlendMode_Name(SkBlendMode);
+
 #endif