Add a "global activate" command to pub.

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

Index: sdk/lib/_internal/pub/lib/src/command/global_activate.dart
diff --git a/sdk/lib/_internal/pub/lib/src/command/global_activate.dart b/sdk/lib/_internal/pub/lib/src/command/global_activate.dart
new file mode 100644
index 0000000000000000000000000000000000000000..5c3e523702551ccd4af9ca58761d92652ded93c0
--- /dev/null
+++ b/sdk/lib/_internal/pub/lib/src/command/global_activate.dart
@@ -0,0 +1,47 @@
+// Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+library pub.command.global_activate;
+
+import 'dart:async';
+
+import '../command.dart';
+import '../utils.dart';
+import '../version.dart';
+
+/// Handles the `global activate` pub command.
+class GlobalActivateCommand extends PubCommand {
+  String get description => "Make a package's executables globally available.";
+  String get usage => "pub global activate <package> [version]";
+  bool get requiresEntrypoint => false;
+  bool get takesArguments => true;
+
+  Future onRun() {
+    // Make sure there is a package.
+    if (commandOptions.rest.isEmpty) {
+      usageError("No package to activate given.");
+    }
+
+    // Don't allow extra arguments.
+    if (commandOptions.rest.length > 2) {
+      var unexpected = commandOptions.rest.skip(2).map((arg) => '"$arg"');
+      var arguments = pluralize("argument", unexpected.length);
+      usageError("Unexpected $arguments ${toSentence(unexpected)}.");
+    }
+
+    var package = commandOptions.rest.first;
+
+    // Parse the version constraint, if there is one.
+    var constraint = VersionConstraint.any;
+    if (commandOptions.rest.length == 2) {
+      try {
+        constraint = new VersionConstraint.parse(commandOptions.rest[1]);
+      } on FormatException catch (error) {
+        usageError(error.message);
+      }
+    }
+
+    return globals.activate(package, constraint);
+  }
+}