Use Shadow DOM to display fallback content for images

LayoutTests/platform/linux/tables/mozilla/bugs/bug4527-expected.txt

Index: LayoutTests/platform/linux/tables/mozilla/bugs/bug4527-expected.txt
diff --git a/LayoutTests/platform/linux/tables/mozilla/bugs/bug4527-expected.txt b/LayoutTests/platform/linux/tables/mozilla/bugs/bug4527-expected.txt
index be3a2bea2d9e91cbb9ad7e13e38571383b0d4e0d..c439fd3628a1e676bb61ed4f9f9bc0083d6216a1 100644
--- a/LayoutTests/platform/linux/tables/mozilla/bugs/bug4527-expected.txt
+++ b/LayoutTests/platform/linux/tables/mozilla/bugs/bug4527-expected.txt
@@ -32,7 +32,7 @@ layer at (0,0) size 800x600
               RenderBlock {INPUT} at (66,3) size 13x13
               RenderText {#text} at (82,1) size 4x19
                 text run at (82,1) width 4: " "
-              RenderImage {IMG} at (86,0) size 46x25
+              RenderBlock {IMG} at (86,0) size 46x25
 layer at (134,8) size 468x60
   RenderPartObject {IFRAME} at (0,0) size 468x60
     layer at (0,0) size 468x60
@@ -48,3 +48,10 @@ layer at (134,8) size 468x60
           RenderText {#text} at (0,0) size 0x0
 layer at (371,82) size 89x16
   RenderBlock {DIV} at (2,3) size 89x16
+layer at (573,78) size 46x25 clip at (574,79) size 44x23
+  RenderBlock {DIV} at (0,0) size 46x25 [border: (1px solid #C0C0C0)]
+    RenderImage {IMG} at (2,2) size 16x16
+layer at (591,80) size 26x20 scrollWidth 59
+  RenderBlock {DIV} at (18,2) size 26x20
+    RenderText {#text} at (0,0) size 59x19
+      text run at (0,0) width 59: "EarthLink"