Restore sanity to RenderLayerStackingNode::shouldBeNormalFlowOnly

This code evolved and grew over the years, but it seems to be trying to compute
something very simple.

Review URL: https://codereview.chromium.org/307933010

git-svn-id: svn://svn.chromium.org/blink/trunk@175704 bbb929c8-8fbe-4397-9dbb-9b2b20218538

third_party/WebKit/LayoutTests/TestExpectations

@@ -226,6 +226,11 @@ crbug.com/378919 [ Linux Android ] fast/forms/suggestion-picker/datetimelocal-su
 # Probably just needs new baseline, but image_diff is failing - investigate that.
 crbug.com/318980 [ Linux x86 ] fast/text/international/hindi-spacing.html [ ImageOnlyFailure ]
 
+Bug(abarth) media/audio-controls-rendering.html [ NeedsRebaseline ]
+Bug(abarth) media/media-controls-clone.html [ NeedsRebaseline ]
+Bug(abarth) media/audio-repaint.html [ NeedsRebaseline ]
+Bug(abarth) media/track/track-cue-rendering-vertical.html [ NeedsRebaseline ]
+
 # Untriaged Mavericks failures
 
 crbug.com/314947 [ Mavericks ] fast/scrolling/scrollbar-tickmarks-hittest.html [ Timeout ]

third_party/WebKit/LayoutTests/inspector/layers/layer-compositing-reasons-expected.txt

@@ -13,7 +13,7 @@ Compositing reasons for div#backface-visibility: assumedOverlap,backfaceVisibili
 Compositing reasons for div#animation: activeAnimation,assumedOverlap
 Compositing reasons for div#transformWithCompositedDescendants: assumedOverlap,transformWithCompositedDescendants
 Compositing reasons for div#opacityWithCompositedDescendants: assumedOverlap,opacityWithCompositedDescendants
-Compositing reasons for div#reflectionWithCompositedDescendants: reflectionWithCompositedDescendants
+Compositing reasons for div#reflectionWithCompositedDescendants: assumedOverlap,reflectionWithCompositedDescendants
 Compositing reasons for div#perspective: assumedOverlap,perspectiveWith3DDescendants
 Compositing reasons for div#preserve3d: assumedOverlap,preserve3DWith3DDescendants
 

third_party/WebKit/Source/core/rendering/RenderLayerStackingNode.cpp

@@ -183,7 +183,6 @@ void RenderLayerStackingNode::updateNormalFlowList()
     ASSERT(m_layerListMutationAllowed);
 
     for (RenderLayer* child = layer()->firstChild(); child; child = child->nextSibling()) {
-        // Ignore non-overflow layers and reflections.
         if (child->stackingNode()->isNormalFlowOnly() && (!layer()->reflectionInfo() || layer()->reflectionInfo()->reflectionLayer() != child)) {
             if (!m_normalFlowList)
                 m_normalFlowList = adoptPtr(new Vector<RenderLayerStackingNode*>);
@@ -205,23 +204,15 @@ void RenderLayerStackingNode::collectLayers(OwnPtr<Vector<RenderLayerStackingNod
 
     layer()->updateDescendantDependentFlags();
 
-    // Overflow layers are just painted by their enclosing layers, so they don't get put in zorder lists.
     if (!isNormalFlowOnly()) {
-        // Determine which buffer the child should be in.
         OwnPtr<Vector<RenderLayerStackingNode*> >& buffer = (zIndex() >= 0) ? posBuffer : negBuffer;
-
-        // Create the buffer if it doesn't exist yet.
         if (!buffer)
             buffer = adoptPtr(new Vector<RenderLayerStackingNode*>);
-
-        // Append ourselves at the end of the appropriate buffer.
         buffer->append(this);
     }
 
-    // Recur into our children to collect more layers, but only if we don't establish a stacking context.
     if (!isStackingContext()) {
         for (RenderLayer* child = layer()->firstChild(); child; child = child->nextSibling()) {
-            // Ignore reflections.
             if (!layer()->reflectionInfo() || layer()->reflectionInfo()->reflectionLayer() != child)
                 child->stackingNode()->collectLayers(posBuffer, negBuffer);
         }
@@ -303,27 +294,11 @@ void RenderLayerStackingNode::updateStackingNodesAfterStyleChange(const RenderSt
         clearZOrderLists();
 }
 
+// FIXME: Rename shouldBeNormalFlowOnly to something more accurate now that CSS
+// 2.1 defines the term "normal flow".
 bool RenderLayerStackingNode::shouldBeNormalFlowOnly() const
 {
-    RenderLayerModelObject* renderer = this->renderer();
-
-    const bool couldBeNormalFlow = renderer->hasOverflowClip()
-        || renderer->hasReflection()
-        || renderer->hasMask()
-        || renderer->isCanvas()
-        || renderer->isVideo()
-        || renderer->isEmbeddedObject()
-        || renderer->isRenderIFrame()
-        || (renderer->style()->specifiesColumns() && !layer()->isRootLayer());
-
-    const bool preventsElementFromBeingNormalFlow = renderer->isPositioned()
-        || renderer->hasTransform()
-        || renderer->hasClipPath()
-        || renderer->hasFilter()
-        || renderer->hasBlendMode()
-        || layer()->isTransparent();
-
-    return couldBeNormalFlow && !preventsElementFromBeingNormalFlow;
+    return !isStackingContext() && !renderer()->isPositioned();
 }
 
 void RenderLayerStackingNode::updateIsNormalFlowOnly()