[turbolizer] Output correct JSON when source contains a backslash.

Previously, we would output \x5c to escape a backslash, but this is
invalid JSON and it would crash Turbolizer. Use \u005c instead.

BUG=

Review-Url: https://codereview.chromium.org/2224913002
Cr-Commit-Position: refs/heads/master@{#38479}

src/ostreams.cc

@@ -61,6 +61,14 @@ std::ostream& PrintUC16(std::ostream& os, uint16_t c, bool (*pred)(uint16_t)) {
   return os << buf;
 }
 
+std::ostream& PrintUC16ForJSON(std::ostream& os, uint16_t c,
+                               bool (*pred)(uint16_t)) {
+  // JSON does not allow \x99; must use \u0099.
+  char buf[10];
+  const char* format = pred(c) ? "%c" : "\\u%04x";
+  snprintf(buf, sizeof(buf), format, c);
+  return os << buf;
+}
 
 std::ostream& PrintUC32(std::ostream& os, int32_t c, bool (*pred)(uint16_t)) {
   if (c <= String::kMaxUtf16CodeUnit) {
@@ -84,7 +92,7 @@ std::ostream& operator<<(std::ostream& os, const AsEscapedUC16ForJSON& c) {
   if (c.value == '\r') return os << "\\r";
   if (c.value == '\t') return os << "\\t";
   if (c.value == '\"') return os << "\\\"";
-  return PrintUC16(os, c.value, IsOK);
+  return PrintUC16ForJSON(os, c.value, IsOK);
 }
 
 

test/cctest/interpreter/bytecode_expectations/RegExpLiterals.golden

@@ -38,7 +38,7 @@ bytecodes: [
   /*   58 S> */ B(Return),
 ]
 constant pool: [
-  "(\x5cw+)\x5cs(\x5cw+)",
+  "(\u005cw+)\u005cs(\u005cw+)",
 ]
 handlers: [
 ]