Improve barback/pub logging.

sdk/lib/_internal/pub/lib/src/log.dart

Index: sdk/lib/_internal/pub/lib/src/log.dart
diff --git a/sdk/lib/_internal/pub/lib/src/log.dart b/sdk/lib/_internal/pub/lib/src/log.dart
index 2d61143e0a430512065c599d6c5d213ff4ec24f0..3ad49089e7a031dca8ec742f53a0931c64ed7c29 100644
--- a/sdk/lib/_internal/pub/lib/src/log.dart
+++ b/sdk/lib/_internal/pub/lib/src/log.dart
@@ -25,6 +25,11 @@ Timer _progressTimer;
 /// progress is done, a single entry will be added to the log for it.
 String _progressMessage;
 
+final _green = getSpecial('\u001b[32m');
+final _red = getSpecial('\u001b[31m');
+final _yellow = getSpecial('\u001b[33m');
+final _none = getSpecial('\u001b[0m');
+
 /// An enum type for defining the different logging levels. By default, [ERROR]
 /// and [WARNING] messages are printed to sterr. [MESSAGE] messages are printed
 /// to stdout, and others are ignored.
@@ -202,6 +207,18 @@ Future progress(String message, Future callback()) {
   return callback().whenComplete(_stopProgress);
 }
 
+/// Wraps [text] in the ANSI escape codes to color it green when on a platform
+/// that supports that.
+String green(text) => "$_green$text$_none";
+
+/// Wraps [text] in the ANSI escape codes to color it red when on a platform
+/// that supports that.
+String red(text) => "$_red$text$_none";
+
+/// Wraps [text] in the ANSI escape codes to color it yellow when on a platform
+/// that supports that.
+String yellow(text) => "$_yellow$text$_none";
+
 /// Stops the running progress indicator, if currently running.
 _stopProgress() {
   if (_progressTimer == null) return;