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

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

Index: sdk/lib/_internal/pub/lib/src/command/cache_repair.dart
diff --git a/sdk/lib/_internal/pub/lib/src/command/cache_repair.dart b/sdk/lib/_internal/pub/lib/src/command/cache_repair.dart
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+++ b/sdk/lib/_internal/pub/lib/src/command/cache_repair.dart
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+// Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+library pub.command.cache_repair;
+
+import 'dart:async';
+
+import '../command.dart';
+import '../exit_codes.dart' as exit_codes;
+import '../io.dart';
+import '../log.dart' as log;
+import '../utils.dart';
+
+/// Handles the `cache repair` pub command.
+class CacheRepairCommand extends PubCommand {
+  String get description => "Reinstall cached packages.";
+  String get usage => "pub cache repair";
+  bool get requiresEntrypoint => false;
+
+  Future onRun() {
+    var successes = 0;
+    var failures = 0;
+
+    // Repair every cached source.
+    return Future.forEach(cache.sources.where(
+        (source) => source.shouldCache), (source) {
+      return source.repairCachedPackages().then((results) {
+        successes += results.first;
+        failures += results.last;
+      });
+    }).then((_) {
+      if (successes > 0) {
+        var packages = pluralize("package", successes);
+        log.message("Reinstalled ${log.green(successes)} $packages.");
+      }
+
+      if (failures > 0) {
+        var packages = pluralize("package", failures);
+        log.message("Failed to reinstall ${log.red(failures)} $packages.");
+      }
+
+      if (successes == 0 && failures == 0) {
+        log.message("No packages in cache, so nothing to repair.");
+      }
+
+      if (failures > 0) return flushThenExit(exit_codes.UNAVAILABLE);
+    });
+  }
+}