Show nicer errors on some server failures.

utils/tests/pub/pub_install_hosted_test.dart

Index: utils/tests/pub/pub_install_hosted_test.dart
diff --git a/utils/tests/pub/pub_install_hosted_test.dart b/utils/tests/pub/pub_install_hosted_test.dart
index af7d08c13aea0086f6d8da0f02d0c052e781326a..77ee457a177290019cc85537611b772f18ac6e52 100644
--- a/utils/tests/pub/pub_install_hosted_test.dart
+++ b/utils/tests/pub/pub_install_hosted_test.dart
@@ -24,6 +24,39 @@ main() {
     run();
   });
 
+  test('fails gracefully if the url does not resolve', () {
+    dir(appPath, [
+      pubspec({
+        "name": "myapp",
+        "dependencies": {
+          "foo": {
+            "hosted": {
+              "name": "foo",
+              "url": "http://pub.invalid"
+            }
+          }
+         }
+      })
+    ]).scheduleCreate();
+
+    schedulePub(args: ['install'],
+        error: const RegExp('Could not resolve URL "http://pub.invalid".'));
+
+    run();
+  });
+
+  test('fails gracefully if the package does not exist', () {
+    servePackages([]);
+
+    appDir([dependency("foo", "1.2.3")]).scheduleCreate();
+
+    schedulePub(args: ['install'],
+        error: const RegExp('Could not find package "foo" on '
+                            'http://localhost:'));
+
+    run();
+  });
+
   test('checks out packages transitively from a pub server', () {
     servePackages([
       package("foo", "1.2.3", [dependency("bar", "2.0.4")]),