Change new List(n) to return fixed length list.

sdk/lib/_internal/compiler/implementation/lib/core_patch.dart

Index: sdk/lib/_internal/compiler/implementation/lib/core_patch.dart
diff --git a/sdk/lib/_internal/compiler/implementation/lib/core_patch.dart b/sdk/lib/_internal/compiler/implementation/lib/core_patch.dart
index caa6b4c0dd3b048ba70d1cb55be8ea53d62e179b..a3d3cf37925a2241450cd6b8c14f6b6cc6966803 100644
--- a/sdk/lib/_internal/compiler/implementation/lib/core_patch.dart
+++ b/sdk/lib/_internal/compiler/implementation/lib/core_patch.dart
@@ -165,16 +165,17 @@ patch class Stopwatch {
 
 // Patch for List implementation.
 patch class List<E> {
-  patch factory List([int length = 0]) {
-    // Explicit type test is necessary to protect Primitives.newGrowableList in
+  patch factory List([int length]) {
+    if (!?length) return Primitives.newGrowableList(0);
+    // Explicit type test is necessary to protect Primitives.newFixedList in
     // unchecked mode.
     if ((length is !int) || (length < 0)) {
       throw new ArgumentError("Length must be a positive integer: $length.");
     }
-    return Primitives.newGrowableList(length);
+    return Primitives.newFixedList(length);
   }
 
-  patch factory List.fixedLength(int length, {E fill: null}) {
+  patch factory List.filled(int length, E fill) {
     // Explicit type test is necessary to protect Primitives.newFixedList in
     // unchecked mode.
     if ((length is !int) || (length < 0)) {