Revert "Fix warnings and hints in the SDK"

sdk/lib/async/stream_impl.dart

Index: sdk/lib/async/stream_impl.dart
diff --git a/sdk/lib/async/stream_impl.dart b/sdk/lib/async/stream_impl.dart
index 92fd7a957f7434e5752a3e9dc96fbf832f5c27e5..3f77294619a6e3d3b1e23f7794fc6b51e8700e95 100644
--- a/sdk/lib/async/stream_impl.dart
+++ b/sdk/lib/async/stream_impl.dart
@@ -998,25 +998,24 @@ class _StreamIteratorImpl<T> implements StreamIterator<T> {
       _current = null;
       _futureOrPrefetch = new _Future<bool>();
       return _futureOrPrefetch;
-    }
-    assert(_state >= _STATE_EXTRA_DATA);
-    switch (_state) {
-      case _STATE_EXTRA_DATA:
-        _state = _STATE_FOUND;
-        _current = _futureOrPrefetch;
-        _futureOrPrefetch = null;
-        _subscription.resume();
-        return new _Future<bool>.immediate(true);
-      case _STATE_EXTRA_ERROR:
-        AsyncError prefetch = _futureOrPrefetch;
-        _clear();
-        return new _Future<bool>.immediateError(prefetch.error,
-                                                prefetch.stackTrace);
-      case _STATE_EXTRA_DONE:
-        _clear();
-        return new _Future<bool>.immediate(false);
-      default:
-        throw "Unreachable";
+    } else {
+      assert(_state >= _STATE_EXTRA_DATA);
+      switch (_state) {
+        case _STATE_EXTRA_DATA:
+          _state = _STATE_FOUND;
+          _current = _futureOrPrefetch;
+          _futureOrPrefetch = null;
+          _subscription.resume();
+          return new _Future<bool>.immediate(true);
+        case _STATE_EXTRA_ERROR:
+          AsyncError prefetch = _futureOrPrefetch;
+          _clear();
+          return new _Future<bool>.immediateError(prefetch.error,
+                                                  prefetch.stackTrace);
+        case _STATE_EXTRA_DONE:
+          _clear();
+          return new _Future<bool>.immediate(false);
+      }
     }
   }