Fix a couple type bugs in dart html and what seems like strange type choices in dart:core

sdk/lib/internal/iterable.dart

Index: sdk/lib/internal/iterable.dart
diff --git a/sdk/lib/internal/iterable.dart b/sdk/lib/internal/iterable.dart
index deb76fc70880839f2313f862098dd65cfb3ef255..87c5f141b32787219504f5a54b413e9dc6596c3c 100644
--- a/sdk/lib/internal/iterable.dart
+++ b/sdk/lib/internal/iterable.dart
@@ -94,7 +94,7 @@ abstract class ListIterable<E> extends IterableBase<E>
     return false;
   }
 
-  dynamic firstWhere(bool test(E element), { Object orElse() }) {
+  E firstWhere(bool test(E element), { E orElse() }) {
     int length = this.length;
     for (int i = 0; i < length; i++) {
       E element = elementAt(i);
@@ -107,7 +107,7 @@ abstract class ListIterable<E> extends IterableBase<E>
     throw IterableElementError.noElement();
   }
 
-  dynamic lastWhere(bool test(E element), { Object orElse() }) {
+  E lastWhere(bool test(E element), { E orElse() }) {
     int length = this.length;
     for (int i = length - 1; i >= 0; i--) {
       E element = elementAt(i);