[wasm] Implement AST printing into an ostream

src/ostreams.h

Index: src/ostreams.h
diff --git a/src/ostreams.h b/src/ostreams.h
index 1c2f38a1539e6ed42736a5f8b6ae82200f27c367..977b5c6f4a48cbeda0e0163b678917779afeeac2 100644
--- a/src/ostreams.h
+++ b/src/ostreams.h
@@ -66,6 +66,12 @@ struct AsEscapedUC16ForJSON {
   uint16_t value;
 };
 
+struct AsHex {
+  explicit AsHex(uint64_t v, uint8_t min_width = 0)
+      : value(v), min_width(min_width) {}
+  uint64_t value;
+  uint8_t min_width;
+};
 
 // Writes the given character to the output escaping everything outside of
 // printable/space ASCII range. Additionally escapes '\' making escaping
@@ -83,6 +89,9 @@ std::ostream& operator<<(std::ostream& os, const AsUC16& c);
 // of printable ASCII range.
 std::ostream& operator<<(std::ostream& os, const AsUC32& c);
 
+// Writes the given number to the output in hexadecimal notation.
+std::ostream& operator<<(std::ostream& os, const AsHex& v);
+
 }  // namespace internal
 }  // namespace v8