Add Dart_PropagateError.

runtime/vm/isolate.cc

Index: runtime/vm/isolate.cc
===================================================================
--- runtime/vm/isolate.cc	(revision 3416)
+++ runtime/vm/isolate.cc	(working copy)
@@ -142,7 +142,7 @@
   result->debugger_ = new Debugger();
   result->debugger_->Initialize(result);
   if (FLAG_trace_isolates) {
-    if (strcmp(name_prefix, "vm-isolate") != 0) {
+    if (name_prefix == NULL || strcmp(name_prefix, "vm-isolate") != 0) {
       OS::Print("[+] Starting isolate:\n"
                 "\tisolate:    %s\n", result->name());
     }
@@ -326,8 +326,7 @@
 
 
 
-RawObject* Isolate::StandardRunLoop() {
-  ASSERT(long_jump_base() != NULL);
+RawError* Isolate::StandardRunLoop() {
   ASSERT(post_message_callback() == &StandardPostMessageCallback);
   ASSERT(close_port_callback() == &StandardClosePortCallback);
 
@@ -344,14 +343,16 @@
           DartLibraryCalls::HandleMessage(
               message->dest_port(), message->reply_port(), msg));
       delete message;
-      if (result.IsUnhandledException()) {
-        return result.raw();
+      if (result.IsError()) {
+        Error& error = Error::Handle();
+        error ^= result.raw();
+        return error.raw();
       }
     }
   }
 
   // Indicates success.
-  return Object::null();
+  return Error::null();
 }