Invalidate CustomScrollbars on having window-inactive selector.

Source/core/frame/FrameView.cpp

Index: Source/core/frame/FrameView.cpp
diff --git a/Source/core/frame/FrameView.cpp b/Source/core/frame/FrameView.cpp
index 79c8bc6ed79e305da0bbcb7175273785db4eb902..73920231e60bb67f904c0c5fd75c65092b9907b0 100644
--- a/Source/core/frame/FrameView.cpp
+++ b/Source/core/frame/FrameView.cpp
@@ -340,6 +340,9 @@ void FrameView::recalculateCustomScrollbarStyle()
 
 void FrameView::invalidateAllCustomScrollbarsOnActiveChanged()
 {
+    if (m_frame && !m_frame->document()->styleEngine()->usesWindowInActiveSelector())
+        return;

[rune, 2015/01/20 13:42:34]

Even if this document doesn't have a :window-inactive selector, it doesn't mean
that the child iframes may not have any. You can skip the styleChanged() on the
scrollbar children, and the recalculateCustomScrollbarStyle, but  not the
recursive call into invalidateAllCustomScrollbarsOnActiveChanged.

[MuVen, 2015/01/20 14:50:11]

Done.

+
     const ChildrenWidgetSet* viewChildren = children();
     for (const RefPtrWillBeMember<Widget>& child : *viewChildren) {
         Widget* widget = child.get();