Support removing dead packages with `pub install`.

utils/tests/pub/pub_install_repo_test.dart

Index: utils/tests/pub/pub_install_repo_test.dart
diff --git a/utils/tests/pub/pub_install_repo_test.dart b/utils/tests/pub/pub_install_repo_test.dart
index fb03dfc9b2cd713333ae1e4ed023d41c653410ca..af7d08c13aea0086f6d8da0f02d0c052e781326a 100644
--- a/utils/tests/pub/pub_install_repo_test.dart
+++ b/utils/tests/pub/pub_install_repo_test.dart
@@ -229,4 +229,104 @@ main() {
 
     run();
   });
+
+  test("removes a dependency that's been removed from the pubspec", () {
+    servePackages([
+      package("foo", "1.0.0"),
+      package("bar", "1.0.0")
+    ]);
+
+    appDir([dependency("foo"), dependency("bar")]).scheduleCreate();
+
+    schedulePub(args: ['install'],
+        output: const RegExp(@"Dependencies installed!$"));
+
+    packagesDir({
+      "foo": "1.0.0",
+      "bar": "1.0.0"
+    }).scheduleValidate();
+
+    appDir([dependency("foo")]).scheduleCreate();
+
+    schedulePub(args: ['install'],
+        output: const RegExp(@"Dependencies installed!$"));
+
+    packagesDir({
+      "foo": "1.0.0",
+      "bar": null
+    }).scheduleValidate();
+
+    run();
+  });
+
+  test("removes a transitive dependency that's no longer depended on", () {
+    servePackages([
+      package("foo", "1.0.0", [dependency("shared-dep")]),
+      package("bar", "1.0.0", [
+        dependency("shared-dep"),
+        dependency("bar-dep")
+      ]),
+      package("shared-dep", "1.0.0"),
+      package("bar-dep", "1.0.0")
+    ]);
+
+    appDir([dependency("foo"), dependency("bar")]).scheduleCreate();
+
+    schedulePub(args: ['install'],
+        output: const RegExp(@"Dependencies installed!$"));
+
+    packagesDir({
+      "foo": "1.0.0",
+      "bar": "1.0.0",
+      "shared-dep": "1.0.0",
+      "bar-dep": "1.0.0",
+    }).scheduleValidate();
+
+    appDir([dependency("foo")]).scheduleCreate();
+
+    schedulePub(args: ['install'],
+        output: const RegExp(@"Dependencies installed!$"));
+
+    packagesDir({
+      "foo": "1.0.0",
+      "bar": null,
+      "shared-dep": "1.0.0",
+      "bar-dep": null,
+    }).scheduleValidate();
+
+    run();
+  });
+
+  test("doesn't update dependencies whose constraints have been removed", () {
+    servePackages([
+      package("foo", "1.0.0", [dependency("shared-dep")]),
+      package("bar", "1.0.0", [dependency("shared-dep", "<2.0.0")]),
+      package("shared-dep", "1.0.0"),
+      package("shared-dep", "2.0.0")
+    ]);
+
+    appDir([dependency("foo"), dependency("bar")]).scheduleCreate();
+
+    schedulePub(args: ['install'],
+        output: const RegExp(@"Dependencies installed!$"));
+
+    packagesDir({
+      "foo": "1.0.0",
+      "bar": "1.0.0",
+      "shared-dep": "1.0.0"
+    }).scheduleValidate();
+
+    appDir([dependency("foo")]).scheduleCreate();
+
+    schedulePub(args: ['install'],
+        output: const RegExp(@"Dependencies installed!$"));
+
+    packagesDir({
+      "foo": "1.0.0",
+      "bar": null,
+      "shared-dep": "1.0.0"
+    }).scheduleValidate();
+
+    run();
+  });
 }