Add support for starting a detached process

runtime/bin/process.cc

Index: runtime/bin/process.cc
diff --git a/runtime/bin/process.cc b/runtime/bin/process.cc
index fecb5aa500abaf990416dfed205cdc54cd9a34a8..52035301c3877989d9e5defa62bc1a87cf503dcb 100644
--- a/runtime/bin/process.cc
+++ b/runtime/bin/process.cc
@@ -65,7 +65,7 @@ void FUNCTION_NAME(Process_Start)(Dart_NativeArguments args) {
   intptr_t process_stdout;
   intptr_t process_stderr;
   intptr_t exit_event;
-  Dart_Handle status_handle = Dart_GetNativeArgument(args, 9);
+  Dart_Handle status_handle = Dart_GetNativeArgument(args, 10);
   Dart_Handle path_handle = Dart_GetNativeArgument(args, 1);
   // The Dart code verifies that the path implements the String
   // interface. However, only builtin Strings are handled by
@@ -118,10 +118,11 @@ void FUNCTION_NAME(Process_Start)(Dart_NativeArguments args) {
       return;
     }
   }
-  Dart_Handle stdin_handle = Dart_GetNativeArgument(args, 5);
-  Dart_Handle stdout_handle = Dart_GetNativeArgument(args, 6);
-  Dart_Handle stderr_handle = Dart_GetNativeArgument(args, 7);
-  Dart_Handle exit_handle = Dart_GetNativeArgument(args, 8);
+  bool detached = DartUtils::GetBooleanValue(Dart_GetNativeArgument(args, 5));
+  Dart_Handle stdin_handle = Dart_GetNativeArgument(args, 6);
+  Dart_Handle stdout_handle = Dart_GetNativeArgument(args, 7);
+  Dart_Handle stderr_handle = Dart_GetNativeArgument(args, 8);
+  Dart_Handle exit_handle = Dart_GetNativeArgument(args, 9);
   intptr_t pid = -1;
   char* os_error_message = NULL;
 
@@ -131,6 +132,7 @@ void FUNCTION_NAME(Process_Start)(Dart_NativeArguments args) {
                                   working_directory,
                                   string_environment,
                                   environment_length,
+                                  detached,
                                   &process_stdout,
                                   &process_stdin,
                                   &process_stderr,
@@ -138,10 +140,12 @@ void FUNCTION_NAME(Process_Start)(Dart_NativeArguments args) {
                                   &exit_event,
                                   &os_error_message);
   if (error_code == 0) {
-    Socket::SetSocketIdNativeField(stdin_handle, process_stdin);
-    Socket::SetSocketIdNativeField(stdout_handle, process_stdout);
-    Socket::SetSocketIdNativeField(stderr_handle, process_stderr);
-    Socket::SetSocketIdNativeField(exit_handle, exit_event);
+    if (!detached) {
+      Socket::SetSocketIdNativeField(stdin_handle, process_stdin);
+      Socket::SetSocketIdNativeField(stdout_handle, process_stdout);
+      Socket::SetSocketIdNativeField(stderr_handle, process_stderr);
+      Socket::SetSocketIdNativeField(exit_handle, exit_event);
+    }
     Process::SetProcessIdNativeField(process, pid);
   } else {
     DartUtils::SetIntegerField(