Fix clipping of content outside the bounds of the window.

sky/tests/clipping/clipping-transforms.sky

Index: sky/tests/clipping/clipping-transforms.sky
diff --git a/sky/tests/lowlevel/filters-expected.sky b/sky/tests/clipping/clipping-transforms.sky
similarity index 57%
copy from sky/tests/lowlevel/filters-expected.sky
copy to sky/tests/clipping/clipping-transforms.sky
index 34757d00717860359561aa2e3c92d11d9623128f..762d06a6ba8b3bf49cfb3c0a1094ae150b6bffa3 100644
--- a/sky/tests/lowlevel/filters-expected.sky
+++ b/sky/tests/clipping/clipping-transforms.sky
@@ -1,7 +1,18 @@
-<foo>
 <import src="../resources/run-after-display.sky" />
 
-<img src="http://storage.googleapis.com/mojo/sky-pngs/9a7b59f74e2bbcd0d0ceee17ead05b0da64a2af7" />
+<style>
+transformer {
+  transform: translateY(-500px);
+}
+child {
+  opacity: 0.5;
+  background-image: linear-gradient(green, yellow);
+  height: 1900px;
+}
+</style>
+<transformer>
+  <child />
+</transformer>
 
 <script>
 import "dart:sky";
@@ -15,4 +26,3 @@ void main() {
   });
 }
 </script>
-</foo>