Use Shadow DOM to display fallback content for images

LayoutTests/platform/linux/fast/forms/input-value-expected.txt

Index: LayoutTests/platform/linux/fast/forms/input-value-expected.txt
diff --git a/LayoutTests/platform/linux/fast/forms/input-value-expected.txt b/LayoutTests/platform/linux/fast/forms/input-value-expected.txt
index ee7670c50d362efbdedb56694ff2729705c97891..584c3f799ae9be01eb40c06d74df576388387918 100644
--- a/LayoutTests/platform/linux/fast/forms/input-value-expected.txt
+++ b/LayoutTests/platform/linux/fast/forms/input-value-expected.txt
@@ -95,7 +95,7 @@ layer at (0,0) size 800x600
                 RenderText {#text} at (1,1) size 209x19
                   text run at (1,1) width 209: "image with value property changed"
               RenderTableCell {TD} at (370,126) size 240x22 [r=5 c=1 rs=1 cs=1]
-                RenderImage {INPUT} at (1,1) size 39x20
+                RenderBlock {INPUT} at (1,1) size 55x20
               RenderTableCell {TD} at (612,126) size 59x22 [r=5 c=2 rs=1 cs=1]
                 RenderText {#text} at (1,1) size 27x19
                   text run at (1,1) width 27: "after"
@@ -208,6 +208,13 @@ layer at (381,166) size 149x16
   RenderBlock {DIV} at (2,3) size 149x16
     RenderText {#text} at (0,0) size 30x16
       text run at (0,0) width 30: "\x{2022}\x{2022}\x{2022}\x{2022}\x{2022}\x{2022}"
+layer at (379,263) size 55x20 clip at (380,264) size 53x18
+  RenderBlock {DIV} at (0,0) size 55x20 [border: (1px solid #C0C0C0)]
+    RenderImage {IMG} at (2,2) size 16x16
+layer at (397,265) size 35x16
+  RenderBlock {DIV} at (18,2) size 35x16
+    RenderText {#text} at (0,0) size 35x16
+      text run at (0,0) width 35: "before"
 layer at (381,314) size 149x16
   RenderBlock {DIV} at (2,3) size 149x16
     RenderText {#text} at (0,0) size 25x16