Always give RenderParts a RenderLayer.

LayoutTests/platform/linux/fast/parser/001-expected.txt

Index: LayoutTests/platform/linux/fast/parser/001-expected.txt
diff --git a/LayoutTests/platform/linux/fast/parser/001-expected.txt b/LayoutTests/platform/linux/fast/parser/001-expected.txt
index e4bfcdee3bc3b6114e98ed00c8384d4f46bad680..0c535973e9e89bf64a02ef5c4444629b96da92f3 100644
--- a/LayoutTests/platform/linux/fast/parser/001-expected.txt
+++ b/LayoutTests/platform/linux/fast/parser/001-expected.txt
@@ -22,7 +22,6 @@ layer at (0,0) size 800x600
         RenderText {#text} at (0,0) size 64x16
           text run at (0,0) width 64: "Pre text"
           text run at (64,0) width 0: " "
-        RenderEmbeddedObject {OBJECT} at (0,16) size 300x300 [bgcolor=#008000]
         RenderText {#text} at (300,304) size 300x32
           text run at (300,304) width 0: " "
           text run at (0,320) width 104: "Also pre text"
@@ -40,3 +39,5 @@ layer at (0,0) size 800x600
           RenderText {#text} at (0,0) size 226x19
             text run at (0,0) width 226: "Now we're back to nonbreaking text."
         RenderText {#text} at (0,0) size 0x0
+layer at (8,152) size 300x300
+  RenderEmbeddedObject {OBJECT} at (0,16) size 300x300 [bgcolor=#008000]