Rip out Settings::fixedPositionCreatesStackingContext

Source/core/rendering/compositing/CompositingReasonFinder.cpp

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "config.h"
 #include "core/rendering/compositing/CompositingReasonFinder.h"
 
 #include "CSSPropertyNames.h"
 #include "HTMLNames.h"
 #include "core/animation/ActiveAnimations.h"
@@ skipping 176 matching lines @@
 bool CompositingReasonFinder::requiresCompositingForPosition(RenderObject* renderer, const RenderLayer* layer, RenderLayer::ViewportConstrainedNotCompositedReason* viewportConstrainedNotCompositedReason, bool* needToRecomputeCompositingRequirements) const
 {
     // position:fixed elements that create their own stacking context (e.g. have an explicit z-index,
     // opacity, transform) can get their own composited layer. A stacking context is required otherwise
     // z-index and clipping will be broken.
     if (!renderer->isPositioned())
         return false;
 
     EPosition position = renderer->style()->position();
     bool isFixed = renderer->isOutOfFlowPositioned() && position == FixedPosition;
+    // FIXME: The isStackingContainer check here is redundant. Fixed position elements are always stacking contexts.
     if (isFixed && !layer->stackingNode()->isStackingContainer())
         return false;
 
     bool isSticky = renderer->isInFlowPositioned() && position == StickyPosition;
     if (!isFixed && !isSticky)
         return false;
 
     // FIXME: acceleratedCompositingForFixedPositionEnabled should probably be renamed acceleratedCompositingForViewportConstrainedPositionEnabled().
     if (Settings* settings = m_renderView.document().settings()) {
         if (!settings->acceleratedCompositingForFixedPositionEnabled())
@@ skipping 77 matching lines @@
 
     return true;
 }
 
 bool CompositingReasonFinder::requiresCompositingForOverflowScrolling(const RenderLayer* layer) const
 {
     return layer->needsCompositedScrolling();
 }
 
 }