Validate packages against their SDK constraints.

utils/pub/command_update.dart

Index: utils/pub/command_update.dart
diff --git a/utils/pub/command_update.dart b/utils/pub/command_update.dart
index 4757049cd26e335d63f0417f9c83d8af6557310f..5c556ce95b580704f4c2da61fe09b39c8338aa22 100644
--- a/utils/pub/command_update.dart
+++ b/utils/pub/command_update.dart
@@ -9,7 +9,7 @@ import 'entrypoint.dart';
 import 'log.dart' as log;
 import 'pub.dart';
 
-/// Handles the `update` pub command. 
+/// Handles the `update` pub command.
 class UpdateCommand extends PubCommand {
   String get description =>
     "Update the current package's dependencies to the latest versions.";
@@ -23,6 +23,8 @@ class UpdateCommand extends PubCommand {
     } else {
       future = entrypoint.updateDependencies(commandOptions.rest);
     }
-    return future.then((_) => log.message("Dependencies updated!"));
+    return future
+        .then((_) => log.message("Dependencies updated!"))
+        .then((_) => entrypoint.validateSdkConstraints());
   }
 }