Escape invalid code points

base/json/string_escape.cc

Index: base/json/string_escape.cc
diff --git a/base/json/string_escape.cc b/base/json/string_escape.cc
index f67fa93bf2648191564eb1a77d46664036b1f41d..9a26ff76c4f4217c8637f2f44babaad0ddc190cd 100644
--- a/base/json/string_escape.cc
+++ b/base/json/string_escape.cc
@@ -91,7 +91,9 @@ bool EscapeJSONStringImpl(const S& str, bool put_in_quotes, std::string* dest) {
 
   for (int32_t i = 0; i < length; ++i) {
     uint32_t code_point;
-    if (!ReadUnicodeCharacter(str.data(), length, &i, &code_point)) {
+    if (!ReadUnicodeCharacter(str.data(), length, &i, &code_point) ||
+        code_point == static_cast<decltype(code_point)>(CBU_SENTINEL) ||
+        !IsValidCharacter(code_point)) {
       code_point = kReplacementCodePoint;
       did_replacement = true;
     }