Use Shadow DOM to display fallback content for images

LayoutTests/platform/linux/fast/dom/34176-expected.txt

Index: LayoutTests/platform/linux/fast/dom/34176-expected.txt
diff --git a/LayoutTests/platform/linux/fast/dom/34176-expected.txt b/LayoutTests/platform/linux/fast/dom/34176-expected.txt
index a63642673bbb81c439b9bc9e9fdac187b9ee8a53..3eb56e2c9a0a910f5b0bed026cb9a9ed73ef5f31 100644
--- a/LayoutTests/platform/linux/fast/dom/34176-expected.txt
+++ b/LayoutTests/platform/linux/fast/dom/34176-expected.txt
@@ -219,7 +219,7 @@ layer at (0,0) size 785x1574
               RenderText {#text} at (739,5) size 30x19
                 text run at (739,5) width 30: "Test"
               RenderInline {SPAN} at (0,0) size 20x19
-                RenderImage {IMG} at (659,0) size 20x20
+                RenderBlock {IMG} at (659,0) size 20x25
         RenderBlock {DIV} at (0,79) size 769x20 [bgcolor=#FF0000]
           RenderText {#text} at (679,0) size 60x19
             text run at (679,0) width 60: "This is a "
@@ -247,7 +247,7 @@ layer at (0,0) size 785x1574
               RenderText {#text} at (741,5) size 28x19
                 text run at (741,5) width 28: "Test"
               RenderInline {SPAN} at (0,0) size 20x19
-                RenderImage {IMG} at (661,0) size 20x20
+                RenderBlock {IMG} at (661,0) size 20x25
         RenderBlock {DIV} at (0,144) size 769x20
           RenderText {#text} at (639,0) size 60x19
             text run at (639,0) width 60: "This is a "
@@ -384,5 +384,11 @@ layer at (0,0) size 785x1574
               text run at (0,0) width 121: "Test 25: : Success"
       RenderBlock (anonymous) at (0,1558) size 769x0
         RenderInline {B} at (0,0) size 0x0
+layer at (667,856) size 20x20 clip at (668,857) size 18x18
+  RenderBlock {DIV} at (0,0) size 20x20 [border: (1px solid #C0C0C0)]
+    RenderImage {IMG} at (2,2) size 16x16
+layer at (669,921) size 20x20 clip at (670,922) size 18x18
+  RenderBlock {DIV} at (0,0) size 20x20 [border: (1px solid #C0C0C0)]
+    RenderImage {IMG} at (2,2) size 16x16
 selection start: position 0 of child 0 {#text} of child 14 {DIV} of child 56 {B} of body
 selection end:   position 4 of child 0 {#text} of child 14 {DIV} of child 56 {B} of body