Add a formatter for folly::StringPiece

test/folly/Range.h

@@ -0,0 +1,17 @@
+// A folly::StringPiece stub.
+
+#include <cstring>
+
+namespace folly {
+class StringPiece {
+ public:
+  explicit StringPiece(const char *s) : data_(s), size_(std::strlen(s)) {}
+
+  const char* data() const { return "foo"; }
+  size_t size() const { return 3; }
+
+ private:
+  const char *data_;
+  size_t size_;
+};
+}