Fix Compositing of Opaque Scrolling Layers and Add Tests

third_party/WebKit/LayoutTests/compositing/overflow/overflow-scroll-with-opaque-background-will-change.html

 <script>

[chrishtr, 2016/09/02 01:19:38]

codereview claims this is identical to
compositing/overflow/overflow-scroll-with-opaque-background.html ?

[Stephen Chennney, 2016/09/06 21:06:21]

It is the same as the test previously named
overflow-scroll-with-opaque-background.html. It's a rename of that test combined
with a re-implementation of that test, since it is really testing the
will-change effect rather than the opaque background case.

 if (window.testRunner)
     window.testRunner.dumpAsText();
 
 function hasOpaqueCompositedScrollingContentsLayer(layer) {
     if (layer.name == "Scrolling Contents Layer")
         return layer.contentsOpaque;
     if (layer.children) {
         for (var i = 0; i < layer.children.length; i++) {
             if (hasOpaqueCompositedScrollingContentsLayer(layer.children[i]))
                 return true;
@@ skipping 27 matching lines @@
 .spacer {
     height: 300px;
 }
 </style>
 <!-- The scroller's Scrolling Contents Layer should be opaque due to the opaque
     color background. Even though the background has a content-box clip there
     is no gap because the scroller has no padding. This means that we will be
     able to draw text with subpixel anti-aliasing.
 -->
 <div id="scroller"><div class="spacer"></div></div>