The expected key is a valid identifier, which is already free of \\, <0x20, ".

src/json-parser.h

Index: src/json-parser.h
diff --git a/src/json-parser.h b/src/json-parser.h
index 61043db307290e5996cda7d5ed98741bba37e74f..9a22738e98d9ae806366d94da030a345b10fed63 100644
--- a/src/json-parser.h
+++ b/src/json-parser.h
@@ -108,10 +108,8 @@ class JsonParser BASE_EMBEDDED {
         const uint8_t* expected_chars = content.ToOneByteVector().start();
         for (int i = 0; i < length; i++) {
           uint8_t c0 = input_chars[i];
-          if (c0 != expected_chars[i] ||
-              c0 == '"' || c0 < 0x20 || c0 == '\\') {
-            return false;
-          }
+          // The expected string has to be free of \, " and characters < 0x20.
+          if (c0 != expected_chars[i]) return false;
         }
         if (input_chars[length] == '"') {
           position_ = position_ + length + 1;