Make servePackages's contents argument saner.

sdk/lib/_internal/pub/test/snapshot/upgrades_snapshot_for_dependency_test.dart

Index: sdk/lib/_internal/pub/test/snapshot/upgrades_snapshot_for_dependency_test.dart
diff --git a/sdk/lib/_internal/pub/test/snapshot/upgrades_snapshot_for_dependency_test.dart b/sdk/lib/_internal/pub/test/snapshot/upgrades_snapshot_for_dependency_test.dart
index f25d4768d781664f257b6a2833da4c626a3e61a6..fdeb83e5ff7d0b64fff512929e728fb69b7ecfb6 100644
--- a/sdk/lib/_internal/pub/test/snapshot/upgrades_snapshot_for_dependency_test.dart
+++ b/sdk/lib/_internal/pub/test/snapshot/upgrades_snapshot_for_dependency_test.dart
@@ -16,16 +16,20 @@ main() {
     servePackages([
       packageMap("foo", "1.2.3", {"bar": "any"}),
       packageMap("bar", "1.2.3")
-    ], contents: [
-      d.dir("lib", [d.file("bar.dart", "final message = 'hello!';")]),
-      d.dir("bin", [
-        d.file("hello.dart", """
+    ], contents: {
+      'foo-1.2.3': [
+        d.dir("bin", [
+          d.file("hello.dart", """
 import 'package:bar/bar.dart';
 
 void main() => print(message);
 """)
-      ])
-    ]);
+        ])
+      ],
+      'bar-1.2.3': [
+        d.dir("lib", [d.file("bar.dart", "final message = 'hello!';")])
+      ]
+    });
 
     d.appDir({"foo": "any"}).create();
 
@@ -36,11 +40,12 @@ void main() => print(message);
     ]).validate();
 
     servePackages([
-      packageMap("foo", "1.2.3", {"bar": "any"}),
       packageMap("bar", "1.2.4")
-    ], contents: [
-      d.dir("lib", [d.file("bar.dart", "final message = 'hello 2!';")]),
-    ], replace: true);
+    ], contents: {
+      'bar-1.2.4': [
+        d.dir("lib", [d.file("bar.dart", "final message = 'hello 2!';")]),
+      ]
+    });
 
     pubUpgrade(output: contains("Precompiled foo:hello."));