Drop background color optimization for composited layers

LayoutTests/compositing/squashing/add-remove-squashed-layers-expected.txt

Index: LayoutTests/compositing/squashing/add-remove-squashed-layers-expected.txt
diff --git a/LayoutTests/compositing/squashing/add-remove-squashed-layers-expected.txt b/LayoutTests/compositing/squashing/add-remove-squashed-layers-expected.txt
index 1c496616cba4c262cee6207c5d98ad77dc0c4c5c..ee3dceee8664157b192e17a836677223dd471840 100644
--- a/LayoutTests/compositing/squashing/add-remove-squashed-layers-expected.txt
+++ b/LayoutTests/compositing/squashing/add-remove-squashed-layers-expected.txt
@@ -15,6 +15,8 @@ CASE 1, original layer tree with overlap1 and overlap2:
               (position 60.00 60.00)
               (bounds 400.00 400.00)
               (contentsOpaque 1)
+              (drawsContent 1)
+              (backgroundColor #808080)
             )
             (GraphicsLayer
               (position 140.00 140.00)
@@ -45,6 +47,8 @@ CASE 2, overlap3 gets added:
               (position 60.00 60.00)
               (bounds 400.00 400.00)
               (contentsOpaque 1)
+              (drawsContent 1)
+              (backgroundColor #808080)
             )
             (GraphicsLayer
               (position 140.00 140.00)
@@ -75,6 +79,8 @@ CASE 3, overlap2 gets removed. Since this does not resize the layer, there shoul
               (position 60.00 60.00)
               (bounds 400.00 400.00)
               (contentsOpaque 1)
+              (drawsContent 1)
+              (backgroundColor #808080)
             )
             (GraphicsLayer
               (position 140.00 140.00)
@@ -105,6 +111,8 @@ CASE 4, overlap1 gets removed:
               (position 60.00 60.00)
               (bounds 400.00 400.00)
               (contentsOpaque 1)
+              (drawsContent 1)
+              (backgroundColor #808080)
             )
             (GraphicsLayer
               (position 300.00 300.00)
@@ -138,6 +146,8 @@ CASE 5, overlap2 gets added back:
               (position 60.00 60.00)
               (bounds 400.00 400.00)
               (contentsOpaque 1)
+              (drawsContent 1)
+              (backgroundColor #808080)
             )
             (GraphicsLayer
               (position 220.00 220.00)
@@ -172,6 +182,8 @@ CASE 6, overlap1 gets added back, and overlap3 gets removed:
               (position 60.00 60.00)
               (bounds 400.00 400.00)
               (contentsOpaque 1)
+              (drawsContent 1)
+              (backgroundColor #808080)
             )
             (GraphicsLayer
               (position 140.00 140.00)