update docs for new/changed textblob apis

Docs-Preview: https://skia.org/?cl=165944
Bug: skia:2664
Change-Id: Ifcd112cae535501d709bc124848e2425d2ec6e5c
Reviewed-on: https://skia-review.googlesource.com/c/165944
Reviewed-by: Cary Clark <caryclark@skia.org>
Commit-Queue: Cary Clark <caryclark@skia.org>
diff --git a/docs/undocumented.bmh b/docs/undocumented.bmh
index 2c31124..a6bf6ee 100644
--- a/docs/undocumented.bmh
+++ b/docs/undocumented.bmh
@@ -354,6 +354,18 @@
 #Subtopic ##
 #Subtopic Engine
 ##
+#Enum SkTextEncoding
+#Const kUTF8_SkTextEncoding 0
+##
+#Const kUTF16_SkTextEncoding 1
+##
+#Const kUTF32_SkTextEncoding 2
+##
+#Const kGlyphID_SkTextEncoding 3
+##
+##
+#Class SkFont
+##
 #Topic ##
 
 #Topic Font_Manager