Support "pub downgrade".

sdk/lib/_internal/pub/lib/src/global_packages.dart

Index: sdk/lib/_internal/pub/lib/src/global_packages.dart
diff --git a/sdk/lib/_internal/pub/lib/src/global_packages.dart b/sdk/lib/_internal/pub/lib/src/global_packages.dart
index 37981460b5746fce2b96e7babb6e0e9470427341..b9bb54881fc29e904daf9b3afdc69add61c7c97e 100644
--- a/sdk/lib/_internal/pub/lib/src/global_packages.dart
+++ b/sdk/lib/_internal/pub/lib/src/global_packages.dart
@@ -5,7 +5,6 @@
 library pub.global_packages;
 
 import 'dart:async';
-import 'dart:convert';
 import 'dart:io';
 
 import 'package:path/path.dart' as p;
@@ -78,10 +77,11 @@ class GlobalPackages {
     }).then((p) {
       package = p;
       // Resolve it and download its dependencies.
-      return resolveVersions(cache.sources, package, lockFile: lockFile);
+      return resolveVersions(SolveType.GET, cache.sources, package,
+          lockFile: lockFile);
     }).then((result) {
       if (!result.succeeded) throw result.error;
-      result.showReport();
+      result.showReport(SolveType.GET);
 
       // Make sure all of the dependencies are locally installed.
       return Future.wait(result.packages.map((id) {