Fix painting of fixed background images in composited layers

LayoutTests/compositing/backgrounds/fixed-backgrounds.html

Index: LayoutTests/compositing/backgrounds/fixed-backgrounds.html
diff --git a/LayoutTests/compositing/backgrounds/fixed-backgrounds.html b/LayoutTests/compositing/backgrounds/fixed-backgrounds.html
new file mode 100644
index 0000000000000000000000000000000000000000..cd48b8165af22df618a9ae113fd319ea856cc2d3
--- /dev/null
+++ b/LayoutTests/compositing/backgrounds/fixed-backgrounds.html
@@ -0,0 +1,35 @@
+<style>

[esprehn, 2014/04/01 22:00:13]

same

+    body {
+        height: 2000px;
+        width: 2000px;
+        overflow: hidden;
+    }
+
+    .box {
+        height: 300px;
+        width: 300px;
+        margin: 20px;
+        margin-left: 10px;
+        background-image: url('../resources/alpha-blocks.png');
+
+        background-size: 500px 300px;
+        background-repeat: no-repeat;
+        background-attachment: fixed;
+        box-shadow: 10px 10px 0px gray; /* inflates composited bounds */
+        border: 4px solid gray;
+        float: left;
+    }
+
+    .composited {
+        -webkit-transform: translateZ(0);
+    }
+</style>
+<script>
+    function doTest()
+    {
+        window.scrollTo(35, 45);
+    }
+    window.addEventListener('load', doTest, false);
+</script>
+<div class="composited box"></div>
+<div class="composited box"></div>