Prefer Dart_SetReturnValue over Dart_PropagateError when it makes sense.

runtime/bin/stdio.cc

Index: runtime/bin/stdio.cc
diff --git a/runtime/bin/stdio.cc b/runtime/bin/stdio.cc
index f0dc923d2d4c9e53fc064b7bb0974eab4ebd54be..c866710e93780954dc937eb9e4cf1e88f32aa9a7 100644
--- a/runtime/bin/stdio.cc
+++ b/runtime/bin/stdio.cc
@@ -47,14 +47,13 @@ void FUNCTION_NAME(Stdin_SetLineMode)(Dart_NativeArguments args) {
 void FUNCTION_NAME(Stdout_GetTerminalSize)(Dart_NativeArguments args) {
   if (!Dart_IsInteger(Dart_GetNativeArgument(args, 0))) {
     OSError os_error(-1, "Invalid argument", OSError::kUnknown);
-    Dart_Handle err = DartUtils::NewDartOSError(&os_error);
-    if (Dart_IsError(err)) Dart_PropagateError(err);
-    Dart_SetReturnValue(args, err);
+    Dart_SetReturnValue(args, DartUtils::NewDartOSError(&os_error));
     return;
   }
   intptr_t fd = DartUtils::GetIntptrValue(Dart_GetNativeArgument(args, 0));
   if (fd != 1 && fd != 2) {
-    Dart_PropagateError(Dart_NewApiError("Terminal fd must be 1 or 2"));
+    Dart_SetReturnValue(args, Dart_NewApiError("Terminal fd must be 1 or 2"));
+    return;
   }
 
   int size[2];