Add offline support to pub install and update.

sdk/lib/_internal/pub/bin/pub.dart

Index: sdk/lib/_internal/pub/bin/pub.dart
diff --git a/sdk/lib/_internal/pub/bin/pub.dart b/sdk/lib/_internal/pub/bin/pub.dart
index 0d6e72a33cf395a999380f5148fd1bb862960973..29a160a9018016686b663223b1573f5b52df236c 100644
--- a/sdk/lib/_internal/pub/bin/pub.dart
+++ b/sdk/lib/_internal/pub/bin/pub.dart
@@ -91,8 +91,6 @@ void main() {
   }
 
   validatePlatform().then((_) {
-    var cache = new SystemCache.withSources(cacheDir);
-
     // Select the command.
     var command = PubCommand.commands[globalOptions.rest[0]];
     if (command == null) {
@@ -103,7 +101,7 @@ void main() {
     }
 
     var commandArgs = globalOptions.rest.sublist(1);
-    command.run(cache, globalOptions, commandArgs);
+    command.run(cacheDir, globalOptions, commandArgs);
   });
 }