Add support for new CSS ::slotted() pseudo element

third_party/WebKit/Source/core/css/resolver/SharedStyleFinder.cpp

Index: third_party/WebKit/Source/core/css/resolver/SharedStyleFinder.cpp
diff --git a/third_party/WebKit/Source/core/css/resolver/SharedStyleFinder.cpp b/third_party/WebKit/Source/core/css/resolver/SharedStyleFinder.cpp
index 0f993d87aea9d8f88aac90c8dc41b76c2ed396b3..0bc7bbf42b3850aade06990549537e6f96757297 100644
--- a/third_party/WebKit/Source/core/css/resolver/SharedStyleFinder.cpp
+++ b/third_party/WebKit/Source/core/css/resolver/SharedStyleFinder.cpp
@@ -278,6 +278,10 @@ bool SharedStyleFinder::canShareStyleWithElement(Element& candidate) const
             return false;
     }
 
+    // TODO(kochi): Investigate cases when assigned slots can share styles.
+    if (element().assignedSlot())

[kochi, 2016/01/07 09:54:09]

I found that this now causes assertion in ElementShadow::assignedSlotFor(),
as if ElementShadow is not for V1 shadow, ElementShadow does not have
slot assignment information.

A workaround is to change this to call assignedSlotForBinding(), but IMHO
we should have an internal API for checking if an element has any assigned
slot.

+        return false;
+
     return true;
 }