[dart:io] Move Platform.ansiSupported to {Stdin,Stdout}.supportsAnsiEscapes

runtime/bin/stdio_macos.cc

Index: runtime/bin/stdio_macos.cc
diff --git a/runtime/bin/stdio_macos.cc b/runtime/bin/stdio_macos.cc
index 5ed3d7e4e11349dfe444b67c0c8f3923a9882585..37ac894583dcdcfa33580481f01ceaacf4484a22 100644
--- a/runtime/bin/stdio_macos.cc
+++ b/runtime/bin/stdio_macos.cc
@@ -83,6 +83,21 @@ bool Stdin::SetLineMode(bool enabled) {
 }
 
 
+static bool TermHasXTerm() {
+  const char* term = getenv("TERM");
+  if (term == NULL) {
+    return false;
+  }
+  return strstr(term, "xterm") != NULL;
+}
+
+
+bool Stdin::AnsiSupported(bool* supported) {
+  *supported = isatty(STDIN_FILENO) && TermHasXTerm();
+  return true;
+}
+
+
 bool Stdout::GetTerminalSize(intptr_t fd, int size[2]) {
   struct winsize w;
   int status = NO_RETRY_EXPECTED(ioctl(fd, TIOCGWINSZ, &w));
@@ -94,6 +109,12 @@ bool Stdout::GetTerminalSize(intptr_t fd, int size[2]) {
   return false;
 }
 
+
+bool Stdout::AnsiSupported(intptr_t fd, bool* supported) {
+  *supported = isatty(fd) && TermHasXTerm();
+  return true;
+}
+
 }  // namespace bin
 }  // namespace dart