Avoid watching files that aren't going to change for "pub serve".

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

Index: sdk/lib/_internal/pub/lib/src/package_graph.dart
diff --git a/sdk/lib/_internal/pub/lib/src/package_graph.dart b/sdk/lib/_internal/pub/lib/src/package_graph.dart
index 634eb5ce5918cbda59e756ed339b564406472cb8..0e2b8e07f9b2f4707f80f937cb41c5f6d6088f5b 100644
--- a/sdk/lib/_internal/pub/lib/src/package_graph.dart
+++ b/sdk/lib/_internal/pub/lib/src/package_graph.dart
@@ -14,10 +14,16 @@ class PackageGraph {
   /// The entrypoint.
   final Entrypoint entrypoint;
 
+  /// The entrypoint's lockfile.
+  ///
+  /// This describes the sources and resolved descriptions of everything in
+  /// [packages].
+  final LockFile lockFile;
+
   /// All transitive dependencies of the entrypoint (including itself).
   final Map<String, Package> packages;
 
-  PackageGraph(this.entrypoint, this.packages);
+  PackageGraph(this.entrypoint, this.lockFile, this.packages);
 
   /// Returns the set of transitive dependencies of the package named
   /// [packageName].