Add offline support to pub install and update.

sdk/lib/_internal/pub/test/pub_test.dart

Index: sdk/lib/_internal/pub/test/pub_test.dart
diff --git a/sdk/lib/_internal/pub/test/pub_test.dart b/sdk/lib/_internal/pub/test/pub_test.dart
index 36071ba35302a136e300aa13aa5884095a3f7070..66eba69d330ba8d27ca7beeb3d9ca02e41dc165a 100644
--- a/sdk/lib/_internal/pub/test/pub_test.dart
+++ b/sdk/lib/_internal/pub/test/pub_test.dart
@@ -27,7 +27,7 @@ final USAGE_STRING = """
               [normal]    Show errors, warnings, and user messages.
               [solver]    Show steps during version resolution.
 
-    -v, --verbose         Shortcut for "--verbosity=all"
+    -v, --verbose         Shortcut for "--verbosity=all".
 
     Available commands:
       cache      Inspect the system cache.
@@ -100,6 +100,7 @@ main() {
             Install the current package's dependencies.
 
             Usage: pub install
+            --[no-]offline    Use cached packages instead of accessing the network.
             ''');
     });
 
@@ -109,9 +110,9 @@ main() {
             Publish the current package to pub.dartlang.org.
 
             Usage: pub publish [options]
-            -n, --dry-run    Validate but do not publish the package                      
-            -f, --force      Publish without confirmation if there are no errors
-                --server     The package server to which to upload this package
+            -n, --dry-run    Validate but do not publish the package.
+            -f, --force      Publish without confirmation if there are no errors.
+                --server     The package server to which to upload this package.
                              (defaults to "https://pub.dartlang.org")
             ''');
     });