Navigation transitions: Hide transition elements by setting CSS opacity rather than display.

Source/web/tests/WebDocumentTest.cpp

Index: Source/web/tests/WebDocumentTest.cpp
diff --git a/Source/web/tests/WebDocumentTest.cpp b/Source/web/tests/WebDocumentTest.cpp
index 923e23d444c9dc8bde4f56677d82097e6c4ac023..186ab316cbc48bc74d80e735f59fdae7506bd68e 100644
--- a/Source/web/tests/WebDocumentTest.cpp
+++ b/Source/web/tests/WebDocumentTest.cpp
@@ -98,7 +98,8 @@ TEST(WebDocumentTest, BeginExitTransition)
 
     // The element should now be hidden.
     transitionStyle = transitionElement->renderStyle();
-    ASSERT_FALSE(transitionStyle);
+    ASSERT_TRUE(transitionStyle);
+    ASSERT_EQ(transitionStyle->opacity(), 0);
 
     // The stylesheet should now have been applied.
     bodyStyle = bodyElement->renderStyle();