Use Shadow DOM to display fallback content for images

LayoutTests/platform/linux/fast/block/float/015-expected.txt

Index: LayoutTests/platform/linux/fast/block/float/015-expected.txt
diff --git a/LayoutTests/platform/linux/fast/block/float/015-expected.txt b/LayoutTests/platform/linux/fast/block/float/015-expected.txt
index 7397db944386bcfe1ac7698a7fb6c3ea557bc8bb..587e961f4108971767c5919ca32f006be80273a1 100644
--- a/LayoutTests/platform/linux/fast/block/float/015-expected.txt
+++ b/LayoutTests/platform/linux/fast/block/float/015-expected.txt
@@ -10,13 +10,27 @@ layer at (0,0) size 800x600
               RenderText {#text} at (4,4) size 4x19
                 text run at (4,4) width 4: " "
             RenderTableCell {TD} at (12,0) size 628x134 [border: (1px inset #808080)] [r=0 c=1 rs=1 cs=1]
-              RenderImage {IMG} at (4,4) size 50x50 [bgcolor=#FFA500]
+              RenderBlock (floating) {IMG} at (4,4) size 50x50 [bgcolor=#FFA500]
               RenderBlock {P} at (4,4) size 620x20
                 RenderText {#text} at (53,0) size 563x19
                   text run at (53,0) width 563: "This text should be flowing past a tall orange rectangle on the left side of the browser window."
               RenderBlock {DIV} at (4,40) size 620x20 [bgcolor=#008000]
                 RenderBR {BR} at (53,0) size 0x19
-              RenderImage {IMG} at (4,60) size 50x50 [bgcolor=#FFA500]
+              RenderBlock (floating) {IMG} at (4,60) size 50x50 [bgcolor=#FFA500]
               RenderBlock {DIV} at (4,110) size 620x20
                 RenderText {#text} at (0,0) size 620x19
                   text run at (0,0) width 620: "This paragraph should appear below the tall orange rectangle above and to the left, and not flow past it."
+layer at (25,13) size 50x50 clip at (26,14) size 48x48
+  RenderBlock {DIV} at (0,0) size 50x50 [border: (1px solid #C0C0C0)]
+    RenderImage {IMG} at (2,2) size 16x16
+layer at (43,15) size 30x20 scrollWidth 47
+  RenderBlock {DIV} at (18,2) size 30x20
+    RenderText {#text} at (0,0) size 47x19
+      text run at (0,0) width 47: "[Image]"
+layer at (25,69) size 50x50 clip at (26,70) size 48x48
+  RenderBlock {DIV} at (0,0) size 50x50 [border: (1px solid #C0C0C0)]
+    RenderImage {IMG} at (2,2) size 16x16
+layer at (43,71) size 30x20 scrollWidth 47
+  RenderBlock {DIV} at (18,2) size 30x20
+    RenderText {#text} at (0,0) size 47x19
+      text run at (0,0) width 47: "[Image]"