Add a "pub global run" command.

sdk/lib/_internal/pub/test/global/run/missing_executable_arg_test.dart

Index: sdk/lib/_internal/pub/test/global/run/missing_executable_arg_test.dart
diff --git a/sdk/lib/_internal/pub/test/global/activate/missing_package_arg_test.dart b/sdk/lib/_internal/pub/test/global/run/missing_executable_arg_test.dart
similarity index 68%
copy from sdk/lib/_internal/pub/test/global/activate/missing_package_arg_test.dart
copy to sdk/lib/_internal/pub/test/global/run/missing_executable_arg_test.dart
index c1f3dc121ccfa6de02148efbf5b088e5c9f1a35b..54eb35c43b729edbf93b022557801c525f733a3f 100644
--- a/sdk/lib/_internal/pub/test/global/activate/missing_package_arg_test.dart
+++ b/sdk/lib/_internal/pub/test/global/run/missing_executable_arg_test.dart
@@ -7,12 +7,12 @@ import '../../test_pub.dart';
 
 main() {
   initConfig();
-  integration('fails if no package was given', () {
-    schedulePub(args: ["global", "activate"],
+  integration('fails if no executable was given', () {
+    schedulePub(args: ["global", "run", "pkg"],
         error: """
-            No package to activate given.
+            Must specify an executable to run.
 
-            Usage: pub global activate <package> [version]
+            Usage: pub global run <package> <executable> [args...]
             -h, --help    Print usage information for this command.
             """,
         exitCode: exit_codes.USAGE);