Add some basic test coverage for layers.

sky/tests/lowlevel/layers.sky

Index: sky/tests/lowlevel/layers.sky
diff --git a/sky/tests/lowlevel/layers.sky b/sky/tests/lowlevel/layers.sky
new file mode 100644
index 0000000000000000000000000000000000000000..f61ec8fb922ab1ff8d64bd775e862b2c18a0b2a6
--- /dev/null
+++ b/sky/tests/lowlevel/layers.sky
@@ -0,0 +1,59 @@
+<sky>
+
+<import src="../resources/run-after-display.sky" as="runAfterDisplay" />
+<style>
+  sky {
+    padding: 10px;
+  }
+  div {
+    width: 50px;
+    height: 50px;
+    white-space: nowrap;
+  }
+</style>
+Transforms
+<div style="transform: translate3d(10px, 10px, 0); background-color: pink;">
+  One
+  <div style="transform: translate3d(10px, 10px, 0); background-color: salmon;">
+    Two
+    <div style="transform: translate3d(10px, 10px, 0); background-color: papayawhip;">
+      Three
+    </div>
+  </div>
+</div>
+
+<div style="position: absolute; right: 50px;">
+  <div style="background-color: red;">
+    1
+  </div>
+  <div style="position: absolute; left: 40px; top: 40px; z-index: 2; background-color: pink;">
+    4
+  </div>
+  <div style="position: absolute; left: 20px; top: 20px; z-index: 0; background-color: salmon;">
+    2
+  </div>
+  <div style="position: absolute; left: 35px; top: 20px; z-index: 1; background-color: papayawhip;">
+    3
+  </div>
+  <div style="background-color: green;">
+    1
+  </div>
+  z-index
+</div>
+
+<div style="position: absolute; bottom: 50px;">
+  Clip-path
+  <div style="background-color: pink; -webkit-clip-path: circle(25px at 25px 25px);">
+    <div style="background-color: salmon; -webkit-clip-path: circle(25px at 35px 35px);">
+      <div style="background-color: papayawhip; -webkit-clip-path: circle(25px at 45px 45px);"></div>
+    </div>
+  </div>
+</div>
+
+<script>
+runAfterDisplay(function() {
+  internals.notifyTestComplete("");
+});
+</script>
+
+</sky>