Drop background color optimization for composited layers

LayoutTests/compositing/squashing/squash-compositing-hover-expected.txt

Index: LayoutTests/compositing/squashing/squash-compositing-hover-expected.txt
diff --git a/LayoutTests/compositing/squashing/squash-compositing-hover-expected.txt b/LayoutTests/compositing/squashing/squash-compositing-hover-expected.txt
index 93618cba478f90cdb4a69e702359e1a271ab3f9e..2cbadace629ff49dc7384695537d104cd915dd33 100644
--- a/LayoutTests/compositing/squashing/squash-compositing-hover-expected.txt
+++ b/LayoutTests/compositing/squashing/squash-compositing-hover-expected.txt
@@ -19,6 +19,8 @@ Case 1, original layer tree:
               (position 100.00 100.00)
               (bounds 100.00 100.00)
               (contentsOpaque 1)
+              (drawsContent 1)
+              (backgroundColor #0000FF)
             )
             (GraphicsLayer
               (position 180.00 180.00)
@@ -48,6 +50,8 @@ Case 2: hovering over the "middle" element (causes that div to become its own co
           (position 100.00 100.00)
           (bounds 100.00 100.00)
           (contentsOpaque 1)
+          (drawsContent 1)
+          (backgroundColor #0000FF)
         )
         (GraphicsLayer
           (children 2
@@ -55,6 +59,8 @@ Case 2: hovering over the "middle" element (causes that div to become its own co
               (position 180.00 180.00)
               (bounds 100.00 100.00)
               (contentsOpaque 1)
+              (drawsContent 1)
+              (backgroundColor #008000)
             )
             (GraphicsLayer
               (position 260.00 260.00)
@@ -86,6 +92,8 @@ Case 3: hovering over the "middle2" element (causes that div to become its own c
               (position 100.00 100.00)
               (bounds 100.00 100.00)
               (contentsOpaque 1)
+              (drawsContent 1)
+              (backgroundColor #0000FF)
             )
             (GraphicsLayer
               (position 180.00 180.00)
@@ -100,6 +108,8 @@ Case 3: hovering over the "middle2" element (causes that div to become its own c
               (position 260.00 260.00)
               (bounds 100.00 100.00)
               (contentsOpaque 1)
+              (drawsContent 1)
+              (backgroundColor #008000)
             )
             (GraphicsLayer
               (position 340.00 340.00)
@@ -131,6 +141,8 @@ Case 4: hovering over the "top" element (causes that div to become its own compo
               (position 100.00 100.00)
               (bounds 100.00 100.00)
               (contentsOpaque 1)
+              (drawsContent 1)
+              (backgroundColor #0000FF)
             )
             (GraphicsLayer
               (position 180.00 180.00)
@@ -143,6 +155,8 @@ Case 4: hovering over the "top" element (causes that div to become its own compo
           (position 340.00 340.00)
           (bounds 100.00 100.00)
           (contentsOpaque 1)
+          (drawsContent 1)
+          (backgroundColor #008000)
         )
       )
     )
@@ -167,6 +181,8 @@ Case 5: back to situation in case 1
               (position 100.00 100.00)
               (bounds 100.00 100.00)
               (contentsOpaque 1)
+              (drawsContent 1)
+              (backgroundColor #0000FF)
             )
             (GraphicsLayer
               (position 180.00 180.00)