Expose <dialog> in the accessibility tree by default.

Source/core/accessibility/AXRenderObject.cpp

Index: Source/core/accessibility/AXRenderObject.cpp
diff --git a/Source/core/accessibility/AXRenderObject.cpp b/Source/core/accessibility/AXRenderObject.cpp
index 30697af9281ed785aba0c541eedfe0bf322add00..c65147e0eebee9134af2dff1216a7103fe45044f 100644
--- a/Source/core/accessibility/AXRenderObject.cpp
+++ b/Source/core/accessibility/AXRenderObject.cpp
@@ -712,6 +712,9 @@ bool AXRenderObject::computeAccessibilityIsIgnored() const
     if (roleValue() == ListItemRole)
         return false;
 
+    if (roleValue() == DialogRole)
+        return false;
+
     // if this element has aria attributes on it, it should not be ignored.
     if (supportsARIAAttributes())
         return false;