[dart:io][windows] Stdout.supportsAnsiEscapes is false when not connected to a terminal

runtime/bin/stdio_win.cc

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #if !defined(DART_IO_DISABLED)
 
 #include "platform/globals.h"
 #if defined(HOST_OS_WINDOWS)
 
 #include "bin/stdio.h"
@@ skipping 74 matching lines @@
   }
   return SetConsoleMode(h, mode);
 }
 
 
 bool Stdin::AnsiSupported(bool* supported) {
   ASSERT(supported != NULL);
   HANDLE h = GetStdHandle(STD_INPUT_HANDLE);
   if (h == INVALID_HANDLE_VALUE) {
     *supported = false;
-    return false;
+    return true;
   }
   DWORD mode;
   if (!GetConsoleMode(h, &mode)) {
     *supported = false;
-    return false;
+    return true;
   }
   *supported = (mode & ENABLE_VIRTUAL_TERMINAL_INPUT) != 0;
   return true;
 }
 
 
 bool Stdout::GetTerminalSize(intptr_t fd, int size[2]) {
   HANDLE h;
   if (fd == 1) {
     h = GetStdHandle(STD_OUTPUT_HANDLE);
@@ skipping 13 matching lines @@
 bool Stdout::AnsiSupported(intptr_t fd, bool* supported) {
   ASSERT(supported != NULL);
   HANDLE h;
   if (fd == 1) {
     h = GetStdHandle(STD_OUTPUT_HANDLE);
   } else {
     h = GetStdHandle(STD_ERROR_HANDLE);
   }
   if (h == INVALID_HANDLE_VALUE) {
     *supported = false;
-    return false;
+    return true;
   }
   DWORD mode;
   if (!GetConsoleMode(h, &mode)) {
     *supported = false;
-    return false;
+    return true;
   }
   *supported = (mode & ENABLE_VIRTUAL_TERMINAL_PROCESSING) != 0;
   return true;
 }
 
 }  // namespace bin
 }  // namespace dart
 
 #endif  // defined(HOST_OS_WINDOWS)
 
 #endif  // !defined(DART_IO_DISABLED)