Improve quoting in pub reproduction command line in pub error message.

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

Index: sdk/lib/_internal/pub/lib/src/command_runner.dart
diff --git a/sdk/lib/_internal/pub/lib/src/command_runner.dart b/sdk/lib/_internal/pub/lib/src/command_runner.dart
index 287a469d3c7afab37ae8cae062586b9023f1c47a..8f04ee183d175c8409ad2375150a2233eca9fe30 100644
--- a/sdk/lib/_internal/pub/lib/src/command_runner.dart
+++ b/sdk/lib/_internal/pub/lib/src/command_runner.dart
@@ -131,10 +131,11 @@ class PubCommandRunner extends CommandRunner {
       if (options['trace']) {
         log.dumpTranscript();
       } else if (!isUserFacingException(error)) {
+        String protectArgument(String x) => x.contains(' ') ? '"$x"' : x;

[nweiz, 2015/03/26 21:46:21]

Can you add a TODO here to do proper shell escaping? Anything less than that is
still going to be a hack that fails sometimes.

Also, nit: we don't use type annotations in the bodies of method calls. 

         log.error("""
 This is an unexpected error. Please run
 
-    pub --trace ${options.arguments.map((arg) => "'$arg'").join(' ')}
+    pub --trace ${options.arguments.map(protectArgument).join(' ')}
 
 and include the results in a bug report on http://dartbug.com/new.
 """);