Clean up (most) uses of Array. Still more to come in the VM corelib code base.

runtime/lib/immutable_map.dart

Index: runtime/lib/immutable_map.dart
===================================================================
--- runtime/lib/immutable_map.dart	(revision 486)
+++ runtime/lib/immutable_map.dart	(working copy)
@@ -37,20 +37,20 @@
 
   Collection<K> getKeys() {
     int numKeys = length;
-    Array<K> array = new Array<K>(numKeys);
+    List<K> list = new List<K>(numKeys);
     for (int i = 0; i < numKeys; i++) {
-      array[i] = kvPairs_[i*2];
+      list[i] = kvPairs_[i*2];
     }
-    return array;
+    return list;
   }
 
   Collection<V> getValues() {
     int numValues = length;
-    Array<K> array = new Array<K>(numValues);
+    List<K> list = new List<K>(numValues);
     for (int i = 0; i < numValues; i++) {
-      array[i] = kvPairs_[i*2 + 1];
+      list[i] = kvPairs_[i*2 + 1];
     }
-    return array;
+    return list;
   }
 
   bool containsKey(K key) {