Make Error.safeToString convert control codes in strings to escapes.

tests/corelib/safe_to_string_test.dart

Index: tests/corelib/safe_to_string_test.dart
diff --git a/tests/corelib/safe_to_string_test.dart b/tests/corelib/safe_to_string_test.dart
index 10be1f73a999a02570b51eeeb37eb9614bb2465b..233eb5dde1e993663227c756e3ab212a5a7c1aad 100644
--- a/tests/corelib/safe_to_string_test.dart
+++ b/tests/corelib/safe_to_string_test.dart
@@ -15,6 +15,16 @@ main() {
 
   Expect.stringEquals(r'"\\\"\n\r"', Error.safeToString('\\"\n\r'));
 
+  Expect.stringEquals(r'"\x00\x01\x02\x03\x04\x05\x06\x07"',
+                      Error.safeToString('\x00\x01\x02\x03\x04\x05\x06\x07'));
+  Expect.stringEquals(r'"\x08\t\n\x0b\x0c\r\x0e\x0f"',
+                      Error.safeToString('\x08\x09\x0a\x0b\x0c\x0d\x0e\x0f'));
+  Expect.stringEquals(r'"\x10\x11\x12\x13\x14\x15\x16\x17"',
+                      Error.safeToString('\x10\x11\x12\x13\x14\x15\x16\x17'));
+  Expect.stringEquals(r'"\x18\x19\x1a\x1b\x1c\x1d\x1e\x1f"',
+                      Error.safeToString('\x18\x19\x1a\x1b\x1c\x1d\x1e\x1f'));
+  Expect.stringEquals('" "', Error.safeToString(" "));
+
   Expect.stringEquals('null', Error.safeToString(null));
   Expect.stringEquals('true', Error.safeToString(true));
   Expect.stringEquals('false', Error.safeToString(false));