[wasm] Implement AST printing into an ostream

src/ostreams.cc

Index: src/ostreams.cc
diff --git a/src/ostreams.cc b/src/ostreams.cc
index 120db257cd19e27fe91068c4dab99dfba709e9f7..45f41bb012089fd52a8beb14d4e6e4ad37cabb9f 100644
--- a/src/ostreams.cc
+++ b/src/ostreams.cc
@@ -97,5 +97,11 @@ std::ostream& operator<<(std::ostream& os, const AsUC32& c) {
   return PrintUC32(os, c.value, IsPrint);
 }
 
+std::ostream& operator<<(std::ostream& os, const AsHex& hex) {
+  char buf[20];
+  snprintf(buf, sizeof(buf), "%.*" PRIx64, hex.min_width, hex.value);
+  return os << buf;
+}
+
 }  // namespace internal
 }  // namespace v8