Re-land "Drop background color optimization for composited layers"

LayoutTests/compositing/squashing/squash-above-fixed-3-expected.txt

Index: LayoutTests/compositing/squashing/squash-above-fixed-3-expected.txt
diff --git a/LayoutTests/compositing/squashing/squash-above-fixed-3-expected.txt b/LayoutTests/compositing/squashing/squash-above-fixed-3-expected.txt
index b6558d7e6aa40a9a48552957d43594ddee2e6b90..e107ac381f1f08b4b3e3ce13db87817c74e14c8c 100644
--- a/LayoutTests/compositing/squashing/squash-above-fixed-3-expected.txt
+++ b/LayoutTests/compositing/squashing/squash-above-fixed-3-expected.txt
@@ -14,21 +14,29 @@ CASE 1, original layer tree:
         (GraphicsLayer
           (bounds 400.00 400.00)
           (contentsOpaque 1)
+          (drawsContent 1)
+          (backgroundColor #808080)
         )
         (GraphicsLayer
           (position 100.00 100.00)
           (bounds 100.00 4000.00)
           (contentsOpaque 1)
+          (drawsContent 1)
+          (backgroundColor #008000)
           (children 2
             (GraphicsLayer
               (position 0.00 50.00)
               (bounds 200.00 100.00)
               (contentsOpaque 1)
+              (drawsContent 1)
+              (backgroundColor #0000FF)
             )
             (GraphicsLayer
               (position 100.00 0.00)
               (bounds 100.00 100.00)
               (contentsOpaque 1)
+              (drawsContent 1)
+              (backgroundColor #00FF00)
             )
           )
         )
@@ -49,21 +57,29 @@ CASE 2, scrolling y by 10 pixels, both the "container" and "inner" should scroll
           (position 0.00 10.00)
           (bounds 400.00 400.00)
           (contentsOpaque 1)
+          (drawsContent 1)
+          (backgroundColor #808080)
         )
         (GraphicsLayer
           (position 100.00 100.00)
           (bounds 100.00 4000.00)
           (contentsOpaque 1)
+          (drawsContent 1)
+          (backgroundColor #008000)
           (children 2
             (GraphicsLayer
               (position 0.00 60.00)
               (bounds 200.00 100.00)
               (contentsOpaque 1)
+              (drawsContent 1)
+              (backgroundColor #0000FF)
             )
             (GraphicsLayer
               (position 100.00 0.00)
               (bounds 100.00 100.00)
               (contentsOpaque 1)
+              (drawsContent 1)
+              (backgroundColor #00FF00)
             )
           )
         )
@@ -84,17 +100,23 @@ CASE 3, scrolling y further so that "inner" no longer overlaps the fixed-pos lay
           (position 0.00 110.00)
           (bounds 400.00 400.00)
           (contentsOpaque 1)
+          (drawsContent 1)
+          (backgroundColor #808080)
         )
         (GraphicsLayer
           (position 100.00 100.00)
           (bounds 200.00 4000.00)
           (drawsContent 1)
           (backgroundColor #008000)
+          (repaint rects
+          )
           (children 1
             (GraphicsLayer
               (position 0.00 160.00)
               (bounds 200.00 100.00)
               (contentsOpaque 1)
+              (drawsContent 1)
+              (backgroundColor #0000FF)
             )
           )
         )