Handle Object.observe notifications for setting Array.length

test/mjsunit/harmony/object-observe.js

Index: test/mjsunit/harmony/object-observe.js
diff --git a/test/mjsunit/harmony/object-observe.js b/test/mjsunit/harmony/object-observe.js
index 4f068424b376831e503cab92bfe510b7a96c21fe..26da547f7c7d9854e67de072c5f794edffa2b67f 100644
--- a/test/mjsunit/harmony/object-observe.js
+++ b/test/mjsunit/harmony/object-observe.js
@@ -333,6 +333,32 @@ observer.assertCallbackRecords([
   { object: obj, name: "1", type: "new" },
 ]);
 
+// Observing array length (including truncation)
+reset();
+var arr = ['a', 'b', 'c', 'd'];
+var arr2 = ['alpha', 'beta'];
+Object.defineProperty(arr, '0', {configurable: false});
+Object.defineProperty(arr, '2', {get: function(){}});
+Object.defineProperty(arr2, '0', {get: function(){}, configurable: false});
+Object.observe(arr, observer.callback);
+Object.observe(arr2, observer.callback);
+arr.length = 2;
+arr.length = 0;
+arr.length = 10;
+arr2.length = 0;
+arr2.length = 1; // no change expected
+Object.deliverChangeRecords(observer.callback);
+observer.assertCallbackRecords([
+  { object: arr, name: '3', type: 'deleted', oldValue: 'd' },
+  // TODO(adamk): oldValue should not be present below
+  { object: arr, name: '2', type: 'deleted', oldValue: undefined },
+  { object: arr, name: 'length', type: 'updated', oldValue: 4 },
+  { object: arr, name: '1', type: 'deleted', oldValue: 'b' },
+  { object: arr, name: 'length', type: 'updated', oldValue: 2 },
+  { object: arr, name: 'length', type: 'updated', oldValue: 1 },
+  { object: arr2, name: '1', type: 'deleted', oldValue: 'beta' },
+  { object: arr2, name: 'length', type: 'updated', oldValue: 2 },
+]);
 
 // Assignments in loops (checking different IC states).
 reset();