SkTextBlob: Begin implementing Extended TextBlob API

include/core/SkPicture.h

Index: include/core/SkPicture.h
diff --git a/include/core/SkPicture.h b/include/core/SkPicture.h
index eb35ef636641abad12ab9a067b5a7e9ae9bdfba6..a0e42c0c17f8749030383ab911b6d0d43b05b31e 100644
--- a/include/core/SkPicture.h
+++ b/include/core/SkPicture.h
@@ -206,10 +206,11 @@ private:
     // V43: Added DRAW_IMAGE and DRAW_IMAGE_RECT opt codes to serialized data
     // V44: Move annotations from paint to drawAnnotation
     // V45: Add invNormRotation to SkLightingShader.
+    // V46: Read and write extended SkTextBlobs.
 
     // Only SKPs within the min/current picture version range (inclusive) can be read.
     static const uint32_t     MIN_PICTURE_VERSION = 35;     // Produced by Chrome M39.
-    static const uint32_t CURRENT_PICTURE_VERSION = 45;
+    static const uint32_t CURRENT_PICTURE_VERSION = 46;
 
     static_assert(MIN_PICTURE_VERSION <= 41,
                   "Remove kFontFileName and related code from SkFontDescriptor.cpp.");