Make pub's binstubs resilient to changes in snapshot format.

sdk/lib/_internal/pub/lib/src/source/hosted.dart

Index: sdk/lib/_internal/pub/lib/src/source/hosted.dart
diff --git a/sdk/lib/_internal/pub/lib/src/source/hosted.dart b/sdk/lib/_internal/pub/lib/src/source/hosted.dart
index 3bb0ea14bfa1ab075996a807def53c3da6c6432a..825a87257384c62e6834b01a23c925754a16ff73 100644
--- a/sdk/lib/_internal/pub/lib/src/source/hosted.dart
+++ b/sdk/lib/_internal/pub/lib/src/source/hosted.dart
@@ -124,30 +124,34 @@ class HostedSource extends CachedSource {
 
   /// Re-downloads all packages that have been previously downloaded into the
   /// system cache from any server.
-  Future<Pair<int, int>> repairCachedPackages() {
-    if (!dirExists(systemCacheRoot)) return new Future.value(new Pair(0, 0));
+  Future<Pair<int, int>> repairCachedPackages() async {
+    if (!dirExists(systemCacheRoot)) return new Pair(0, 0);
 
     var successes = 0;
     var failures = 0;
 
-    return Future.wait(listDir(systemCacheRoot).map((serverDir) {
+    for (var serverDir in listDir(systemCacheRoot)) {
       var url = _directoryToUrl(path.basename(serverDir));
       var packages = _getCachedPackagesInDirectory(path.basename(serverDir));
       packages.sort(Package.orderByNameAndVersion);
-      return Future.wait(packages.map((package) {
-        return _download(url, package.name, package.version, package.dir)
-            .then((_) {
+      for (var package in packages) {
+        try {
+          await _download(url, package.name, package.version, package.dir);
           successes++;
-        }).catchError((error, stackTrace) {
+        } catch (error, stackTrace) {
           failures++;
           var message = "Failed to repair ${log.bold(package.name)} "
               "${package.version}";
           if (url != defaultUrl) message += " from $url";
           log.error("$message. Error:\n$error");
           log.fine(stackTrace);
-        });
-      }));
-    })).then((_) => new Pair(successes, failures));
+
+          tryDeleteEntry(package.dir);
+        }
+      }
+    }
+
+    return new Pair(successes, failures);
   }
 
   /// Gets all of the packages that have been downloaded into the system cache