Support display: contents for elements, first-line and first-letter pseudos.

third_party/WebKit/Source/core/dom/NodeComputedStyle.h

Index: third_party/WebKit/Source/core/dom/NodeComputedStyle.h
diff --git a/third_party/WebKit/Source/core/dom/NodeComputedStyle.h b/third_party/WebKit/Source/core/dom/NodeComputedStyle.h
index 8ba226ca765bf86c36cae8d95a18a37742c764de..55bff9a4d77e094dc137a3403a5576c7e1835f7d 100644
--- a/third_party/WebKit/Source/core/dom/NodeComputedStyle.h
+++ b/third_party/WebKit/Source/core/dom/NodeComputedStyle.h
@@ -25,6 +25,7 @@
 #ifndef NodeComputedStyle_h
 #define NodeComputedStyle_h
 
+#include "core/dom/Element.h"
 #include "core/dom/LayoutTreeBuilderTraversal.h"
 #include "core/dom/Node.h"
 #include "core/dom/shadow/InsertionPoint.h"
@@ -41,12 +42,19 @@ inline const ComputedStyle* Node::computedStyle() const {
 inline ComputedStyle* Node::mutableComputedStyle() const {
   if (LayoutObject* layoutObject = this->layoutObject())
     return layoutObject->mutableStyle();
-  // <option> and <optgroup> can be styled even if they don't get layout
-  // objects, so they store their style internally and return it through
-  // nonLayoutObjectComputedStyle().  We check here explicitly to avoid the
-  // virtual call in the common case.
-  if (isHTMLOptGroupElement(*this) || isHTMLOptionElement(this))
-    return nonLayoutObjectComputedStyle();
+
+  if (isElementNode()) {
+    if (ComputedStyle* style = toElement(this)->mutableDisplayContentsStyle())
+      return style;
+
+    // <option> and <optgroup> can be styled even if they don't get layout
+    // objects, so they store their style internally and return it through
+    // nonLayoutObjectComputedStyle().  We check here explicitly to avoid the
+    // virtual call in the common case.
+    if (isHTMLOptGroupElement(*this) || isHTMLOptionElement(this))
+      return nonLayoutObjectComputedStyle();

[rune, 2016/11/01 07:12:23]

Now we will have two different ways of persisting ComputedStyle without a
LayoutObject. Wouldn't it be better to use the same method for option/optgroup
and display:contents?

[emilio, 2016/11/01 15:46:31]

Yep, this was already in my mind. I'd prefer to do this as a followup though, if
that's fine.

+  }
+
   return 0;
 }