Add “pub cache repair” to forcibly re-install previously cached packages.

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

Index: sdk/lib/_internal/pub/lib/src/command/cache.dart
diff --git a/sdk/lib/_internal/pub/lib/src/command/cache.dart b/sdk/lib/_internal/pub/lib/src/command/cache.dart
index 93897fae11ecfb7679a44c667959aaa51e13efa7..63d027bd22be146e4fec8e9f5637c28ab6bf9f4b 100644
--- a/sdk/lib/_internal/pub/lib/src/command/cache.dart
+++ b/sdk/lib/_internal/pub/lib/src/command/cache.dart
@@ -7,6 +7,7 @@ library pub.command.cache;
 import '../command.dart';
 import 'cache_add.dart';
 import 'cache_list.dart';
+import 'cache_repair.dart';
 
 /// Handles the `cache` pub command.
 class CacheCommand extends PubCommand {
@@ -15,6 +16,7 @@ class CacheCommand extends PubCommand {
 
   final subcommands = {
     "add": new CacheAddCommand(),
-    "list": new CacheListCommand()
+    "list": new CacheListCommand(),
+    "repair": new CacheRepairCommand()
   };
 }