Fix Error.prototype.toString to be ES5 conform.

src/messages.js

Index: src/messages.js
diff --git a/src/messages.js b/src/messages.js
index 4a81e95b64169aca3c8886d6ff6e025fa3eada73..c1873c51fbcbe912657a3a8242132c407a50c07f 100644
--- a/src/messages.js
+++ b/src/messages.js
@@ -83,7 +83,7 @@ function IsNativeErrorObject(obj) {
 // objects between script tags in a browser setting.
 function ToStringCheckErrorObject(obj) {
   if (IsNativeErrorObject(obj)) {
-    return %_CallFunction(obj, errorToString);
+    return %_CallFunction(obj, ErrorToString);
   } else {
     return ToString(obj);
   }
@@ -1146,28 +1146,32 @@ $Error.captureStackTrace = captureStackTrace;
 
 %SetProperty($Error.prototype, 'message', '', DONT_ENUM);
 
-// Global list of error objects visited during errorToString. This is
+// Global list of error objects visited during ErrorToString. This is
 // used to detect cycles in error toString formatting.
 const visited_errors = new InternalArray();
 const cyclic_error_marker = new $Object();
 
-function errorToStringDetectCycle(error) {
+function ErrorToStringDetectCycle(error) {
   if (!%PushIfAbsent(visited_errors, error)) throw cyclic_error_marker;
   try {
     var type = error.type;

[Lasse Reichstein, 2011/10/26 07:40:24]

The spec doesn't say anything about reading .type. If that's something we use
internally, we should first check (somehow) whether it is an internal error
(i.e., we control .type) before reading or using it, so we don't trigger a
user-visible action (e.g., a getter on "type").

[Michael Starzinger, 2011/10/26 09:30:20]

I agree, the spec says nothing about any "type" or "arguments" property. I think
the only correct solution would be to hide those two properties completely from
the JavaScript world. But that is outside the scope of this CL.

+    var name = error.name

[Lasse Reichstein, 2011/10/26 07:40:24]

According to the spec, we should do ToString on name before reading message.

[Michael Starzinger, 2011/10/26 09:30:20]

Done.

+    var message = error.message;
     var hasMessage = %_CallFunction(error, "message", ObjectHasOwnProperty);
     if (type && !hasMessage) {
-      var formatted = FormatMessage(%NewMessageObject(type, error.arguments));
-      return error.name + ": " + formatted;
+      message = FormatMessage(%NewMessageObject(type, error.arguments));
     }
-    var message = hasMessage ? (": " + error.message) : "";
-    return error.name + message;
+    name = IS_UNDEFINED(name) ? "Error" : TO_STRING_INLINE(name);
+    message = IS_UNDEFINED(message) ? "" : TO_STRING_INLINE(message);
+    if (name === "") return message;
+    if (message === "") return name;
+    return name + ": " + message;
   } finally {
     visited_errors.length = visited_errors.length - 1;
   }
 }
 
-function errorToString() {
+function ErrorToString() {
   if (IS_NULL_OR_UNDEFINED(this) && !IS_UNDETECTABLE(this)) {
     throw MakeTypeError("called_on_null_or_undefined",
                         ["Error.prototype.toString"]);
@@ -1177,7 +1181,7 @@ function errorToString() {
   function isCyclicErrorMarker(o) { return o === cyclic_error_marker; }
 
   try {
-    return errorToStringDetectCycle(this);
+    return ErrorToStringDetectCycle(this);
   } catch(e) {
     // If this error message was encountered already return the empty
     // string for it instead of recursively formatting it.
@@ -1189,7 +1193,7 @@ function errorToString() {
 }
 
 
-InstallFunctions($Error.prototype, DONT_ENUM, ['toString', errorToString]);
+InstallFunctions($Error.prototype, DONT_ENUM, ['toString', ErrorToString]);
 
 // Boilerplate for exceptions for stack overflows. Used from
 // Isolate::StackOverflow().