Disable style sharing outside tests.

third_party/WebKit/Source/core/dom/Element.cpp

Index: third_party/WebKit/Source/core/dom/Element.cpp
diff --git a/third_party/WebKit/Source/core/dom/Element.cpp b/third_party/WebKit/Source/core/dom/Element.cpp
index 406ccfc9b05755070367a8ca7eaf22f6ba2fb7c2..3b88e39e285cd23fd8897fb1233698818b278aee 100644
--- a/third_party/WebKit/Source/core/dom/Element.cpp
+++ b/third_party/WebKit/Source/core/dom/Element.cpp
@@ -4232,6 +4232,8 @@ void Element::AddPropertyToPresentationAttributeStyle(
 }
 
 bool Element::SupportsStyleSharing() const {
+  if (!RuntimeEnabledFeatures::styleSharingEnabled())
+    return false;
   if (!IsStyledElement() || !ParentOrShadowHostElement())
     return false;
   // If the element has inline style it is probably unique.