Added support for isolate unhandled exceptions.

runtime/lib/isolate.cc

Index: runtime/lib/isolate.cc
diff --git a/runtime/lib/isolate.cc b/runtime/lib/isolate.cc
index 7219bda38b16d78209b6de077e7da862ef5cc014..3bb05c39c41f455c29fee41a908089792657e005 100644
--- a/runtime/lib/isolate.cc
+++ b/runtime/lib/isolate.cc
@@ -91,8 +91,7 @@ static void ShutdownIsolate(uword parameter) {
     Error& error = Error::Handle();
     error = isolate->object_store()->sticky_error();
     if (!error.IsNull()) {
-      OS::PrintErr("%s\n", error.ToErrorCString());
-      exit(255);
+      OS::PrintErr("in ShutdownIsolate: %s\n", error.ToErrorCString());
     }
   }
   {
@@ -388,6 +387,14 @@ static RawObject* Spawn(NativeArguments* arguments, SpawnState* state) {
     Exceptions::PropagateError(Error::Cast(port));
   }
 
+  // If specified, set the new isolate's uncaught exception handler.
+  ASSERT(arguments->NativeArgCount() == 2);
+  const Object& arg = Object::Handle(arguments->NativeArgAt(1));
+  if (!arg.IsNull()) {
+    const Instance& callback = Instance::Cast(arg);
+    state->isolate()->object_store()->set_unhandled_exception_closure(callback);
+  }
+
   // Start the new isolate.
   state->isolate()->set_spawn_data(reinterpret_cast<uword>(state));
   state->isolate()->message_handler()->Run(
@@ -398,7 +405,7 @@ static RawObject* Spawn(NativeArguments* arguments, SpawnState* state) {
 }
 
 
-DEFINE_NATIVE_ENTRY(isolate_spawnFunction, 1) {
+DEFINE_NATIVE_ENTRY(isolate_spawnFunction, 2) {
   GET_NATIVE_ARGUMENT(Instance, closure, arguments->NativeArgAt(0));
   bool throw_exception = false;
   Function& func = Function::Handle();
@@ -427,7 +434,7 @@ DEFINE_NATIVE_ENTRY(isolate_spawnFunction, 1) {
 }
 
 
-DEFINE_NATIVE_ENTRY(isolate_spawnUri, 1) {
+DEFINE_NATIVE_ENTRY(isolate_spawnUri, 2) {
   GET_NATIVE_ARGUMENT(String, uri, arguments->NativeArgAt(0));
 
   // Canonicalize the uri with respect to the current isolate.