First stab at "pub run" command.

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 0b93b3f3df26cee40c5b536b0bb67f05d22ec3c5..178ebd7376824461e52cda4460ce8c003c5ab4a3 100644
--- a/sdk/lib/_internal/pub/lib/src/log.dart
+++ b/sdk/lib/_internal/pub/lib/src/log.dart
@@ -225,6 +225,11 @@ void dumpTranscript() {
 /// returned by [callback] completes. If anything else is logged during this
 /// (include another call to [progress]) that cancels the progress.
 Future progress(String message, Future callback()) {
+  // If messages are not output, don't output progress either.
+  if (_loggers[Level.MESSAGE] == null) {
+    return callback();

[nweiz, 2014/05/29 19:30:09]

Nit: This looks like it can fit on the previous line.

[Bob Nystrom, 2014/05/30 18:17:47]

Done.

+  }
+
   _stopProgress();
   _progress = new Progress(message);
   return callback().whenComplete(() {
@@ -333,6 +338,16 @@ void showAll() {
   _loggers[Level.FINE]    = _logToStderrWithLabel;
 }
 
+/// Sets the verbosity to "error", which only logs errors.
+void showError() {
+  _loggers[Level.ERROR]   = _logToStderrWithLabel;
+  _loggers[Level.WARNING] = null;
+  _loggers[Level.MESSAGE] = null;
+  _loggers[Level.IO]      = null;
+  _loggers[Level.SOLVER]  = null;
+  _loggers[Level.FINE]    = null;
+}
+
 /// Log function that prints the message to stdout.
 void _logToStdout(Entry entry) {
   _logToStream(stdout, entry, showLabel: false);