move annotations to canvas virtual

include/core/SkWriter32.h

Index: include/core/SkWriter32.h
diff --git a/include/core/SkWriter32.h b/include/core/SkWriter32.h
index 1e7ec6d3483e12cf4f49db56734ea8f453fcb4e1..a2c6f5d4721c74847ba35ddc31e21fc9889aed3c 100644
--- a/include/core/SkWriter32.h
+++ b/include/core/SkWriter32.h
@@ -206,6 +206,18 @@ public:
      */
     static size_t WriteStringSize(const char* str, size_t len = (size_t)-1);
 
+    void writeData(const SkData* data) {
+        uint32_t len = data ? SkToU32(data->size()) : 0;
+        this->write32(len);
+        if (data) {
+            this->writePad(data->data(), len);
+        }
+    }
+
+    static size_t WriteDataSize(const SkData* data) {
+        return 4 + SkAlign4(data ? data->size() : 0);
+    }
+
     /**
      *  Move the cursor back to offset bytes from the beginning.
      *  offset must be a multiple of 4 no greater than size().