Add a "pub global run" command.

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

Index: sdk/lib/_internal/pub/lib/src/command.dart
diff --git a/sdk/lib/_internal/pub/lib/src/command.dart b/sdk/lib/_internal/pub/lib/src/command.dart
index ccd54d0ea3d66c24aa87c4f618087b6223f0adf0..daa1a6b23a0be52989c2f1b239c77dfdff19c20a 100644
--- a/sdk/lib/_internal/pub/lib/src/command.dart
+++ b/sdk/lib/_internal/pub/lib/src/command.dart
@@ -191,7 +191,10 @@ abstract class PubCommand {
       entrypoint = new Entrypoint(path.current, cache);
     }
 
-    return syncFuture(onRun);
+    return syncFuture(onRun).catchError((error) {
+      if (error is UsageException) error.bindUsage(_getUsage());
+      throw error;
+    });
   }
 
   /// Override this to perform the specific command.
@@ -214,13 +217,6 @@ abstract class PubCommand {
     log.message('$description\n\n${_getUsage()}');
   }
 
-  // TODO(rnystrom): Use this in other places handle usage failures.
-  /// Throw a [UsageException] for a usage error of this command with
-  /// [message].
-  void usageError(String message) {
-    throw new UsageException(message, _getUsage());
-  }
-
   /// Parses a user-supplied integer [intString] named [name].
   ///
   /// If the parsing fails, prints a usage message and exits.