[C++] The first commit for C++ version

16 tests out of 169 are passing.
diff --git a/string_piece_test.cc b/string_piece_test.cc
new file mode 100644
index 0000000..8e16731
--- /dev/null
+++ b/string_piece_test.cc
@@ -0,0 +1,17 @@
+#include "string_piece.h"
+
+#include <assert.h>
+
+#include <unordered_set>
+
+using namespace std;
+
+int main() {
+  unordered_set<StringPiece> sps;
+  sps.insert(STRING_PIECE("foo"));
+  sps.insert(STRING_PIECE("foo"));
+  sps.insert(STRING_PIECE("bar"));
+  assert(sps.size() == 2);
+  assert(sps.count(STRING_PIECE("foo")) == 1);
+  assert(sps.count(STRING_PIECE("bar")) == 1);
+}