[dart:io] Adds Platform.ansiSupported

runtime/bin/platform_win.cc

Index: runtime/bin/platform_win.cc
diff --git a/runtime/bin/platform_win.cc b/runtime/bin/platform_win.cc
index 71a274346d439320e45cbe43a029e26a2cf21091..f181ea005002850c29eb709634dcb0febe62f082 100644
--- a/runtime/bin/platform_win.cc
+++ b/runtime/bin/platform_win.cc
@@ -65,12 +65,15 @@ class PlatformWin {
     saved_output_cp_ = GetConsoleOutputCP();
     SetConsoleOutputCP(CP_UTF8);
 
+    ansi_supported_ = true;
     HANDLE out = GetStdHandle(STD_OUTPUT_HANDLE);
     if ((out != INVALID_HANDLE_VALUE) &&
         GetConsoleMode(out, &saved_console_out_mode_)) {
       const DWORD request =
           saved_console_out_mode_ | ENABLE_VIRTUAL_TERMINAL_PROCESSING;
-      SetConsoleMode(out, request);
+      ansi_supported_ = ansi_supported_ && SetConsoleMode(out, request);
+    } else {
+      ansi_supported_ = false;
     }
 
     HANDLE in = GetStdHandle(STD_INPUT_HANDLE);
@@ -78,7 +81,9 @@ class PlatformWin {
         GetConsoleMode(in, &saved_console_in_mode_)) {
       const DWORD request =
           saved_console_in_mode_ | ENABLE_VIRTUAL_TERMINAL_INPUT;
-      SetConsoleMode(in, request);
+      ansi_supported_ = ansi_supported_ && SetConsoleMode(in, request);
+    } else {
+      ansi_supported_ = false;
     }
   }
 
@@ -100,11 +105,14 @@ class PlatformWin {
     }
   }
 
+  static bool ansi_supported() { return ansi_supported_; }
+
  private:
   static Mutex* platform_win_mutex_;
   static int saved_output_cp_;
   static DWORD saved_console_out_mode_;
   static DWORD saved_console_in_mode_;
+  static bool ansi_supported_;
 
   static void InvalidParameterHandler(const wchar_t* expression,
                                       const wchar_t* function,
@@ -123,6 +131,7 @@ int PlatformWin::saved_output_cp_ = -1;
 DWORD PlatformWin::saved_console_out_mode_ = 0;
 DWORD PlatformWin::saved_console_in_mode_ = 0;
 Mutex* PlatformWin::platform_win_mutex_ = NULL;
+bool PlatformWin::ansi_supported_ = false;
 
 bool Platform::Initialize() {
   PlatformWin::InitOnce();
@@ -219,6 +228,11 @@ const char* Platform::ResolveExecutablePath() {
 }
 
 
+bool Platform::AnsiSupported() {
+  return PlatformWin::ansi_supported();
+}
+
+
 void Platform::Exit(int exit_code) {
   // TODO(zra): Remove once VM shuts down cleanly.
   ::dart::private_flag_windows_run_tls_destructors = false;