Cleanup VM error handling.

runtime/bin/dartutils.cc

Index: runtime/bin/dartutils.cc
diff --git a/runtime/bin/dartutils.cc b/runtime/bin/dartutils.cc
index 3e107f8bbfc7e24e854c774bdad4dbc50deed64d..5de42acc9f4ca06374055d9840a76cf7dd0baea4 100644
--- a/runtime/bin/dartutils.cc
+++ b/runtime/bin/dartutils.cc
@@ -778,6 +778,7 @@ Dart_Handle DartUtils::NewDartOSError() {
 Dart_Handle DartUtils::NewDartOSError(OSError* os_error) {
   // Create a dart:io OSError object with the information retrieved from the OS.
   Dart_Handle type = GetDartType(kIOLibURL, "OSError");
+  ASSERT(!Dart_IsError(type));
   Dart_Handle args[2];
   args[0] = NewString(os_error->message());
   args[1] = Dart_NewInteger(os_error->code());
@@ -791,6 +792,7 @@ Dart_Handle DartUtils::NewDartExceptionWithOSError(const char* library_url,
                                                    Dart_Handle os_error) {
   // Create a Dart Exception object with a message and an OSError.
   Dart_Handle type = GetDartType(library_url, exception_name);
+  ASSERT(!Dart_IsError(type));
   Dart_Handle args[2];
   args[0] = NewString(message);
   args[1] = os_error;
@@ -803,6 +805,7 @@ Dart_Handle DartUtils::NewDartExceptionWithMessage(const char* library_url,
                                                    const char* message) {
   // Create a Dart Exception object with a message.
   Dart_Handle type = GetDartType(library_url, exception_name);
+  ASSERT(!Dart_IsError(type));
   if (message != NULL) {
     Dart_Handle args[1];
     args[0] = NewString(message);
@@ -832,7 +835,7 @@ Dart_Handle DartUtils::NewDartIOException(const char* exception_name,
 
 
 Dart_Handle DartUtils::NewInternalError(const char* message) {
-  return NewDartExceptionWithMessage(kCoreLibURL, "InternalError", message);
+  return NewDartExceptionWithMessage(kCoreLibURL, "_InternalError", message);
 }