fix(repeater) resize scroller correctly,

There was some recursion inside VirtualRepeatController.prototype.virtualRepeatUpdate_ which was causing the scroller not to shrink properly when items were removed.

Fixes #5027. Closes #5031.

In addition, in onDemand mode an undefined length would stop the container from sizing correctly. An undefined length will now be changed to zero.#
It could also possibly fix #4950 and may be a better solution than #5009, but I haven't yet tested it against that issue.#
fixes #5027#   (use "git push" to publish your local commits)

src/components/virtualRepeat/virtual-repeater.js

@@ -574,21 +574,21 @@ VirtualRepeatController.prototype.getItemSize = function() {
  * @private
  */
 VirtualRepeatController.prototype.virtualRepeatUpdate_ = function(items, oldItems) {
-  var itemsLength = items ? items.length : 0;
+  var itemsLength = items && items.length || 0;
   var lengthChanged = false;
 
-  if (itemsLength !== this.itemsLength) {
-    lengthChanged = true;
-    this.itemsLength = itemsLength;
-  }
-
   // If the number of items shrank, scroll up to the top.
   if (this.items && itemsLength < this.items.length && this.container.getScrollOffset() !== 0) {
     this.items = items;
     this.container.resetScroll();
     return;
   }
 
+  if (itemsLength !== this.itemsLength) {
+    lengthChanged = true;
+    this.itemsLength = itemsLength;
+  }
+
   this.items = items;
   if (items !== oldItems || lengthChanged) {
     this.updateIndexes_();

src/components/virtualRepeat/virtual-repeater.spec.js

@@ -408,6 +408,74 @@ describe('<md-virtual-repeat>', function() {
     expect(getRepeated().length).toBe(numItemRenderers);
   });
 
+  it('should resize the scroller correctly when item length changes (vertical)', function() {
+    scope.items = createItems(200);
+    createRepeater();
+    scope.$apply();
+    $$rAF.flush();
+    expect(sizer[0].offsetHeight).toBe(200 * ITEM_SIZE);
+
+    // Scroll down half way
+    scroller[0].scrollTop = 100 * ITEM_SIZE;
+    scroller.triggerHandler('scroll');
+    scope.$apply();
+    $$rAF.flush();
+
+    // Remove some items
+    scope.items = createItems(20);
+    scope.$apply();
+    $$rAF.flush();
+    expect(scroller[0].scrollTop).toBe(0);
+    expect(sizer[0].offsetHeight).toBe(20 * ITEM_SIZE);
+
+    // Scroll down half way
+    scroller[0].scrollTop = 10 * ITEM_SIZE;
+    scroller.triggerHandler('scroll');
+    scope.$apply();
+    $$rAF.flush();
+
+    // Add more items
+    scope.items = createItems(250);
+    scope.$apply();
+    $$rAF.flush();
+    expect(scroller[0].scrollTop).toBe(100);
+    expect(sizer[0].offsetHeight).toBe(250 * ITEM_SIZE);
+  });
+
+  it('should resize the scroller correctly when item length changes (horizontal)', function() {
+    container.attr({'md-orient-horizontal': ''});
+    scope.items = createItems(200);
+    createRepeater();
+    scope.$apply();
+    $$rAF.flush();
+    expect(sizer[0].offsetWidth).toBe(200 * ITEM_SIZE);
+
+    // Scroll right half way
+    scroller[0].scrollLeft = 100 * ITEM_SIZE;
+    scroller.triggerHandler('scroll');
+    scope.$apply();
+    $$rAF.flush();
+
+    // Remove some items
+    scope.items = createItems(20);
+    scope.$apply();
+    $$rAF.flush();
+    expect(scroller[0].scrollLeft).toBe(0);
+    expect(sizer[0].offsetWidth).toBe(20 * ITEM_SIZE);
+
+    // Scroll right half way
+    scroller[0].scrollLeft = 10 * ITEM_SIZE;
+    scroller.triggerHandler('scroll');
+    scope.$apply();
+    $$rAF.flush();
+
+    // Add more items
+    scope.items = createItems(250);
+    scope.$apply();
+    $$rAF.flush();
+    expect(sizer[0].offsetWidth).toBe(250 * ITEM_SIZE);
+  });
+
   it('should update topIndex when scrolling', function() {
     container.attr({'md-top-index': 'topIndex'});
     scope.items = createItems(NUM_ITEMS);