Refactor removeRange.

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

Index: sdk/lib/_internal/compiler/implementation/lib/js_array.dart
diff --git a/sdk/lib/_internal/compiler/implementation/lib/js_array.dart b/sdk/lib/_internal/compiler/implementation/lib/js_array.dart
index c3065eb261c1e0cd8c9de9c8ab5b1e2a7c76c40f..7902ed906516ffbbc06d6bbdffe613672769b057 100644
--- a/sdk/lib/_internal/compiler/implementation/lib/js_array.dart
+++ b/sdk/lib/_internal/compiler/implementation/lib/js_array.dart
@@ -216,29 +216,20 @@ class JSArray<E> extends Interceptor implements List<E>, JSIndexable {
 
   E max([int compare(E a, E b)]) => IterableMixinWorkaround.max(this, compare);
 
-  void removeRange(int start, int length) {
-    checkGrowable(this, 'removeRange');
-    if (length == 0) {
-      return;
-    }
-    checkNull(start); // TODO(ahe): This is not specified but co19 tests it.
-    checkNull(length); // TODO(ahe): This is not specified but co19 tests it.
-    if (start is !int) throw new ArgumentError(start);
-    if (length is !int) throw new ArgumentError(length);
-    if (length < 0) throw new ArgumentError(length);
-    var receiverLength = this.length;
-    if (start < 0 || start >= receiverLength) {
-      throw new RangeError.value(start);
+  void removeRange(int start, int end) {
+    int receiverLength = this.length;
+    if (start < 0 || start > receiverLength) {
+      throw new RangeError.range(start, 0, receiverLength);
     }
-    if (start + length > receiverLength) {
-      throw new RangeError.value(start + length);
+    if (end < start || end > receiverLength) {
+      throw new RangeError.range(end, start, receiverLength);
     }
     Arrays.copy(this,
-                start + length,
+                end,
                 this,
                 start,
-                receiverLength - length - start);
-    this.length = receiverLength - length;
+                receiverLength - end);
+    this.length = receiverLength - (end - start);
   }
 
   void setRange(int start, int end, List<E> from, [int startFrom = 0]) {