SkTextBlob: Begin implementing Extended TextBlob API

src/core/SkTextBlobRunIterator.h

Index: src/core/SkTextBlobRunIterator.h
diff --git a/src/core/SkTextBlobRunIterator.h b/src/core/SkTextBlobRunIterator.h
index 42bbac0bc9d647693483deb38a89ce4491b4ef35..db99dd0d640b8656ef56af26f89160c2c0a82be9 100644
--- a/src/core/SkTextBlobRunIterator.h
+++ b/src/core/SkTextBlobRunIterator.h
@@ -28,6 +28,11 @@ public:
     const SkPoint& offset() const;
     void applyFontToPaint(SkPaint*) const;
     SkTextBlob::GlyphPositioning positioning() const;
+    bool isExtended() const;
+    uint32_t* clusterBuffer() const;
+    uint32_t textSize() const;
+    char* textBuffer() const;
+
     bool isLCD() const;
 
 private: