Add Shell::PrintErr and expose it in the d8 shell as printErr

src/d8.cc

Index: src/d8.cc
diff --git a/src/d8.cc b/src/d8.cc
index 69072a22e4fcde79672050c0b99c9b05f9749866..202ecbd0e3aefe917166ebe52ae096aca6f9ea20 100644
--- a/src/d8.cc
+++ b/src/d8.cc
@@ -933,19 +933,11 @@ void Shell::RealmSharedSet(Local<String> property,
   data->realm_shared_.Reset(isolate, value);
 }
 
-
-void Shell::Print(const v8::FunctionCallbackInfo<v8::Value>& args) {
-  Write(args);
-  printf("\n");
-  fflush(stdout);
-}
-
-
-void Shell::Write(const v8::FunctionCallbackInfo<v8::Value>& args) {
+void WriteToFile(FILE* file, const v8::FunctionCallbackInfo<v8::Value>& args) {
   for (int i = 0; i < args.Length(); i++) {
     HandleScope handle_scope(args.GetIsolate());
     if (i != 0) {
-      printf(" ");
+      fprintf(file, " ");
     }
 
     // Explicitly catch potential exceptions in toString().
@@ -963,14 +955,32 @@ void Shell::Write(const v8::FunctionCallbackInfo<v8::Value>& args) {
     }
 
     v8::String::Utf8Value str(str_obj);
-    int n = static_cast<int>(fwrite(*str, sizeof(**str), str.length(), stdout));
+    int n = static_cast<int>(fwrite(*str, sizeof(**str), str.length(), file));
     if (n != str.length()) {
       printf("Error in fwrite\n");
-      Exit(1);
+      Shell::Exit(1);
     }
   }
 }
 
+void WriteAndFlush(FILE* file,
+                   const v8::FunctionCallbackInfo<v8::Value>& args) {
+  WriteToFile(file, args);
+  fprintf(file, "\n");
+  fflush(file);
+}
+
+void Shell::Print(const v8::FunctionCallbackInfo<v8::Value>& args) {
+  WriteAndFlush(stdout, args);
+}
+
+void Shell::PrintErr(const v8::FunctionCallbackInfo<v8::Value>& args) {
+  WriteAndFlush(stderr, args);
+}
+
+void Shell::Write(const v8::FunctionCallbackInfo<v8::Value>& args) {
+  WriteToFile(stdout, args);
+}
 
 void Shell::Read(const v8::FunctionCallbackInfo<v8::Value>& args) {
   String::Utf8Value file(args[0]);
@@ -1387,6 +1397,10 @@ Local<ObjectTemplate> Shell::CreateGlobalTemplate(Isolate* isolate) {
           .ToLocalChecked(),
       FunctionTemplate::New(isolate, Print));
   global_template->Set(
+      String::NewFromUtf8(isolate, "printErr", NewStringType::kNormal)
+          .ToLocalChecked(),
+      FunctionTemplate::New(isolate, PrintErr));
+  global_template->Set(
       String::NewFromUtf8(isolate, "write", NewStringType::kNormal)
           .ToLocalChecked(),
       FunctionTemplate::New(isolate, Write));