add some more autosize demos for testing

Author: mmalerba

src/demo-app/virtual-scroll/virtual-scroll-demo.html

@@ -1,12 +1,30 @@
 <h2>Autosize</h2>
 
+<h3>Uniform size</h3>
 <cdk-virtual-scroll-viewport class="demo-viewport" autosize>
   <div *cdkVirtualFor="let size of fixedSizeData; let i = index" class="demo-item"
        [style.height.px]="size">
     Item #{{i}} - ({{size}}px)
   </div>
 </cdk-virtual-scroll-viewport>
 
+<h3>Increasing size</h3>
+<cdk-virtual-scroll-viewport class="demo-viewport" autosize>
+  <div *cdkVirtualFor="let size of increasingSizeData; let i = index" class="demo-item"
+       [style.height.px]="size">
+    Item #{{i}} - ({{size}}px)
+  </div>
+</cdk-virtual-scroll-viewport>
+
+<h3>Decreasing size</h3>
+<cdk-virtual-scroll-viewport class="demo-viewport" autosize>
+  <div *cdkVirtualFor="let size of decreasingSizeData; let i = index" class="demo-item"
+       [style.height.px]="size">
+    Item #{{i}} - ({{size}}px)
+  </div>
+</cdk-virtual-scroll-viewport>
+
+<h3>Random size</h3>
 <cdk-virtual-scroll-viewport class="demo-viewport" autosize>
   <div *cdkVirtualFor="let size of randomData; let i = index" class="demo-item"
        [style.height.px]="size">

src/demo-app/virtual-scroll/virtual-scroll-demo.ts

@@ -17,5 +17,7 @@ import {Component, ViewEncapsulation} from '@angular/core';
 })
 export class VirtualScrollDemo {
   fixedSizeData = Array(10000).fill(50);
+  increasingSizeData = Array(10000).fill(0).map((_, i) => i / 10000 * 300);
+  decreasingSizeData = Array(10000).fill(0).map((_, i) => (10000 - i) / 10000 * 300);
   randomData = Array(10000).fill(0).map(() => Math.round(Math.random() * 100));
 }