Don't double-escape in strings in the VM Service, and don't use \u0000 to determine the string lengt

runtime/vm/object.h

Index: runtime/vm/object.h
diff --git a/runtime/vm/object.h b/runtime/vm/object.h
index 164ef23f464776873048bb48030bbf109324efda..ade7b9e321b688a636170c5e3820424e0501b663 100644
--- a/runtime/vm/object.h
+++ b/runtime/vm/object.h
@@ -5586,8 +5586,15 @@ class String : public Instance {
 
   void ToUTF8(uint8_t* utf8_array, intptr_t array_len) const;
 
-  // Produces a quoted, escaped, (possibly) truncated string.
-  const char* ToUserCString(intptr_t max_len) const;
+  // Creates a UTF-8, NUL-terminated string in the current zone. The size of the
+  // created string in UTF-8 code units (bytes) is answered in 'length'; this
+  // can be longer than strlen of the result when the string has internal NULs.
+  // For the truncating version, 'max_length' is in UTF-16 code units, and will
+  // be rounded down if necessary to prevent splitting a surrogate pair.
+  const char* ToCString(intptr_t *length) const;
+  const char* ToCStringTruncated(intptr_t max_len,
+                                 bool* did_truncate,
+                                 intptr_t *length) const;
 
   // Copies the string characters into the provided external array
   // and morphs the string object into an external string object.
@@ -5733,9 +5740,6 @@ class String : public Instance {
                            CallbackType new_symbol,
                            Snapshot::Kind kind);
 
-  intptr_t EscapedString(char* buffer, int max_len) const;
-  intptr_t EscapedStringLen(intptr_t tooLong) const;
-
   FINAL_HEAP_OBJECT_IMPLEMENTATION(String, Instance);
 
   friend class Class;