[json parser] add position to error message.

src/messages.h

Index: src/messages.h
diff --git a/src/messages.h b/src/messages.h
index c8a072761fb8cc5dfe57552986f5adc4682cdc58..af1538a1aa44a7e03509531c4eb0145d6a95bd0b 100644
--- a/src/messages.h
+++ b/src/messages.h
@@ -406,6 +406,10 @@ class CallSite {
   T(InvalidLhsInPrefixOp,                                                      \
     "Invalid left-hand side expression in prefix operation")                   \
   T(InvalidRegExpFlags, "Invalid flags supplied to RegExp constructor '%'")    \
+  T(JsonParseUnexpectedEOS, "Unexpected end of JSON input")                    \
+  T(JsonParseUnexpectedToken, "Unexpected token % in JSON at position %")      \
+  T(JsonParseUnexpectedTokenNumber, "Unexpected number in JSON at position %") \
+  T(JsonParseUnexpectedTokenString, "Unexpected string in JSON at position %") \
   T(LabelRedeclaration, "Label '%' has already been declared")                 \
   T(MalformedArrowFunParamList, "Malformed arrow function parameter list")     \
   T(MalformedRegExp, "Invalid regular expression: /%/: %")                     \