Remove unnecessary throws in growablearray.

runtime/lib/growable_array.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 class GrowableObjectArray<T> implements List<T> {
   factory GrowableObjectArray._uninstantiable() {
     throw const UnsupportedOperationException(
         "GrowableObjectArray can only be allocated by the VM");
   }
 
   T removeAt(int index) {
     if (index is! int) throw new IllegalArgumentException(index);
     T result = this[index];
     int newLength = this.length - 1;
     Arrays.copy(this,
                 index + 1,
                 this,
                 index,
                 newLength - index);
     this.length = newLength;
     return result;
   }
-  
+
   void setRange(int start, int length, List<T> from, [int startFrom = 0]) {
     if (length < 0) {
       throw new IllegalArgumentException("negative length $length");
     }
     Arrays.copy(from, startFrom, this, start, length);
   }
 
   void removeRange(int start, int length) {
     if (length == 0) {
       return;
@@ skipping 98 matching lines @@
   }
 
   void addAll(Collection<T> collection) {
     for (T elem in collection) {
       add(elem);
     }
   }
 
   T removeLast() {
     var len = length - 1;
-    if (len < 0) {
-      throw new IndexOutOfRangeException(-1);
-    }
     var elem = this[len];
     this[len] = null;
     _setLength(len);
     return elem;
   }
 
   T last() {
-    if (length === 0) {
-      throw new IndexOutOfRangeException(-1);
-    }
     return this[length - 1];
   }
 
   int indexOf(T element, [int start = 0]) {
     return Arrays.indexOf(this, element, start, length);
   }
 
   int lastIndexOf(T element, [int start = null]) {
     if (start === null) start = length - 1;
     return Arrays.lastIndexOf(this, element, start);
@@ skipping 75 matching lines @@
   T next() {
     if (!hasNext()) {
       throw const NoMoreElementsException();
     }
     return _array[_pos++];
   }
 
   final GrowableObjectArray<T> _array;
   int _pos;
 }