Support "pub downgrade".

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

Index: sdk/lib/_internal/pub/lib/src/command/get.dart
diff --git a/sdk/lib/_internal/pub/lib/src/command/get.dart b/sdk/lib/_internal/pub/lib/src/command/get.dart
index 3c066fdbabae3c7ebde91eac83233c9c7ff45add..7394e0c76ae1312e8c9037d4f175af677c3e4be3 100644
--- a/sdk/lib/_internal/pub/lib/src/command/get.dart
+++ b/sdk/lib/_internal/pub/lib/src/command/get.dart
@@ -7,6 +7,7 @@ library pub.command.get;
 import 'dart:async';
 
 import '../command.dart';
+import '../solver/version_solver.dart';
 
 /// Handles the `get` pub command.
 class GetCommand extends PubCommand {
@@ -25,6 +26,7 @@ class GetCommand extends PubCommand {
   }
 
   Future onRun() {
-    return entrypoint.acquireDependencies(dryRun: commandOptions['dry-run']);
+    return entrypoint.acquireDependencies(SolveType.GET,
+        dryRun: commandOptions['dry-run']);
   }
 }