Use Shadow DOM to display fallback content for images

LayoutTests/platform/linux/fast/block/float/017-expected.txt

Index: LayoutTests/platform/linux/fast/block/float/017-expected.txt
diff --git a/LayoutTests/platform/linux/fast/block/float/017-expected.txt b/LayoutTests/platform/linux/fast/block/float/017-expected.txt
index 2fb8155f8775bb022b79ac86e4e0dd0ec2de89fb..e8654689ea65ad22e9572d1fb0b3d7e5ab108b67 100644
--- a/LayoutTests/platform/linux/fast/block/float/017-expected.txt
+++ b/LayoutTests/platform/linux/fast/block/float/017-expected.txt
@@ -7,7 +7,7 @@ layer at (0,0) size 800x600
         RenderImage {IMG} at (2,2) size 450x29 [bgcolor=#FFFF00]
         RenderText {#text} at (0,0) size 0x0
         RenderBR {BR} at (0,0) size 0x0
-        RenderImage {IMG} at (2,31) size 250x125 [bgcolor=#FFA500]
+        RenderBlock (floating) {IMG} at (2,31) size 250x125 [bgcolor=#FFA500]
         RenderText {#text} at (255,31) size 197x139
           text run at (255,31) width 197: "Theme Park Roller Coaster is an"
           text run at (255,51) width 164: "excellent game that lets you"
@@ -25,3 +25,10 @@ layer at (0,0) size 800x600
           RenderText {#text} at (2,22) size 158x19
             text run at (2,22) width 158: "Second non-breaking line."
         RenderText {#text} at (0,0) size 0x0
+layer at (10,39) size 250x125 clip at (11,40) size 248x123
+  RenderBlock {DIV} at (0,0) size 250x125 [border: (1px solid #C0C0C0)]
+    RenderImage {IMG} at (2,2) size 16x16
+layer at (28,41) size 230x20
+  RenderBlock {DIV} at (18,2) size 230x20
+    RenderText {#text} at (0,0) size 166x19
+      text run at (0,0) width 166: "Theme Park Roller Coaster"