Run with colored output even within "pub run".

test/io.dart

Index: test/io.dart
diff --git a/test/io.dart b/test/io.dart
index 09bd31df2c4de4a59f98d13dbd3b560aded397e4..7ba9eb04fe78aa819f705815fee1bb2c05713f33 100644
--- a/test/io.dart
+++ b/test/io.dart
@@ -16,23 +16,29 @@ String _computePackageDir() =>
     p.dirname(p.dirname(_libraryPath(#unittest.test.io)));
 
 /// Runs the unittest executable with the package root set properly.
-ProcessResult runUnittest(List<String> args, {String workingDirectory}) {
+ProcessResult runUnittest(List<String> args, {String workingDirectory,
+    Map<String, String> environment}) {
   var allArgs = [
     p.join(packageDir, 'bin/unittest.dart'),
     "--package-root=${p.join(packageDir, 'packages')}"
   ]..addAll(args);
 
+  if (environment == null) environment = {};
+  environment.putIfAbsent("_UNITTEST_USE_COLOR", () => "false");
+
   // TODO(nweiz): Use ScheduledProcess once it's compatible.
-  return runDart(allArgs, workingDirectory: workingDirectory);
+  return runDart(allArgs, workingDirectory: workingDirectory,
+      environment: environment);
 }
 
 /// Runs Dart.
-ProcessResult runDart(List<String> args, {String workingDirectory}) {
+ProcessResult runDart(List<String> args, {String workingDirectory,
+    Map<String, String> environment}) {
   var allArgs = Platform.executableArguments.toList()..addAll(args);
 
   // TODO(nweiz): Use ScheduledProcess once it's compatible.
   return Process.runSync(Platform.executable, allArgs,
-      workingDirectory: workingDirectory);
+      workingDirectory: workingDirectory, environment: environment);
 }
 
 /// Returns the path to the library named [libraryName].