Fix nested border radius with composited child.

third_party/WebKit/LayoutTests/compositing/overflow/border-radius-on-grandparent-composited-grandchild.html

+<style>
+.outermost {
+        border: 4px solid #000;
+        width: 200px;
+        height: 200px;
+        border-radius: 40px;
+        overflow: hidden;
+}
+
+.middle {
+  border: 4px solid #888;
+  background-color: #008;
+  width: 200px;
+  height: 200px;
+  position: relative;
+  left: 100px;
+  top: 100px;
+  overflow: hidden;
+}
+
+.inner {
+  border: 4px solid #AAA;
+        width: 80px;
+        height: 400px;
+        background-color: #080;
+        position: relative;
+  left: 20px;
+  top: -100px;
+  will-change: transform;
+}
+</style>
+
+<div class="outermost">
+        <div class="middle">
+    <div class="inner">
+    </div>
+  </div>
+</div>
+