[turbofan] Improve JSON output

src/ostreams.h

Index: src/ostreams.h
diff --git a/src/ostreams.h b/src/ostreams.h
index 840f341551632a4d21e5e747be1a524f0f1cc752..6f8600e7b1c522b6d3aab16be4bc63e74fe42cb5 100644
--- a/src/ostreams.h
+++ b/src/ostreams.h
@@ -55,12 +55,20 @@ struct AsReversiblyEscapedUC16 {
   uint16_t value;
 };
 
+struct AsEscapedUC16ForJSON {
+  explicit AsEscapedUC16ForJSON(uint16_t v) : value(v) {}
+  uint16_t value;
+};
+
 
 // Writes the given character to the output escaping everything outside of
 // printable/space ASCII range. Additionally escapes '\' making escaping
 // reversible.
 std::ostream& operator<<(std::ostream& os, const AsReversiblyEscapedUC16& c);
 
+// Same as AsReversiblyEscapedUC16 with additional escaping of \n, \r, " and '.
+std::ostream& operator<<(std::ostream& os, const AsEscapedUC16ForJSON& c);
+
 // Writes the given character to the output escaping everything outside
 // of printable ASCII range.
 std::ostream& operator<<(std::ostream& os, const AsUC16& c);