Adding Angular's DI package & Dart unittests which test it.

third_party/pkg/di/lib/errors.dart

Index: third_party/pkg/di/lib/errors.dart
diff --git a/third_party/pkg/di/lib/errors.dart b/third_party/pkg/di/lib/errors.dart
new file mode 100644
index 0000000000000000000000000000000000000000..8967d0e519f40888e69fca93c9c0b9def77d558b
--- /dev/null
+++ b/third_party/pkg/di/lib/errors.dart
@@ -0,0 +1,9 @@
+part of di;
+
+class NoProviderError extends ArgumentError {
+  NoProviderError(message) : super(message);
+}
+
+class CircularDependencyError extends ArgumentError {
+  CircularDependencyError(message) : super(message);
+}