Remove support for CompositingReasonPositionSticky

Our support for position: sticky isn't even in the experimental feature set. We
shouldn't be burning time during every frame checking whether any RenderLayers
have sticky position.

R=esprehn@chromium.org

Review URL: https://codereview.chromium.org/328263002

git-svn-id: svn://svn.chromium.org/blink/trunk@175992 bbb929c8-8fbe-4397-9dbb-9b2b20218538

third_party/WebKit/Source/core/rendering/compositing/CompositingReasonFinder.cpp

@@ -136,9 +136,6 @@ CompositingReasons CompositingReasonFinder::nonStyleDeterminedDirectReasons(cons
             directReasons |= CompositingReasonOverflowScrollingTouch;
     }
 
-    if (requiresCompositingForPositionSticky(renderer, layer))
-        directReasons |= CompositingReasonPositionSticky;
-
     if (requiresCompositingForPositionFixed(renderer, layer, 0))
         directReasons |= CompositingReasonPositionFixed;
 
@@ -156,22 +153,6 @@ bool CompositingReasonFinder::requiresCompositingForAnimation(RenderStyle* style
     return style->shouldCompositeForCurrentAnimations();
 }
 
-bool CompositingReasonFinder::requiresCompositingForPosition(RenderObject* renderer, const RenderLayer* layer, RenderLayer::ViewportConstrainedNotCompositedReason* viewportConstrainedNotCompositedReason) const
-{
-    return requiresCompositingForPositionSticky(renderer, layer) || requiresCompositingForPositionFixed(renderer, layer, viewportConstrainedNotCompositedReason);
-}
-
-bool CompositingReasonFinder::requiresCompositingForPositionSticky(RenderObject* renderer, const RenderLayer* layer) const
-{
-    if (!(m_compositingTriggers & ViewportConstrainedPositionedTrigger))
-        return false;
-    if (renderer->style()->position() != StickyPosition)
-        return false;
-    // FIXME: This probably isn't correct for accelerated overflow scrolling. crbug.com/361723
-    // Instead it should return false only if the layer is not inside a scrollable region.
-    return !layer->enclosingOverflowClipLayer(ExcludeSelf);
-}
-
 bool CompositingReasonFinder::requiresCompositingForPositionFixed(RenderObject* renderer, const RenderLayer* layer, RenderLayer::ViewportConstrainedNotCompositedReason* viewportConstrainedNotCompositedReason) const
 {
     if (!(m_compositingTriggers & ViewportConstrainedPositionedTrigger))

third_party/WebKit/Source/core/rendering/compositing/CompositingReasonFinder.h

@@ -27,7 +27,7 @@ public:
     bool hasOverflowScrollTrigger() const;
 
     bool requiresCompositingForScrollableFrame() const;
-    bool requiresCompositingForPosition(RenderObject*, const RenderLayer*, RenderLayer::ViewportConstrainedNotCompositedReason*) const;
+    bool requiresCompositingForPositionFixed(RenderObject*, const RenderLayer*, RenderLayer::ViewportConstrainedNotCompositedReason*) const;
 
 private:
     bool isMainFrame() const;
@@ -37,8 +37,6 @@ private:
     bool requiresCompositingForTransform(RenderObject*) const;
     bool requiresCompositingForFilters(RenderObject*) const;
     bool requiresCompositingForAnimation(RenderStyle*) const;
-    bool requiresCompositingForPositionSticky(RenderObject*, const RenderLayer*) const;
-    bool requiresCompositingForPositionFixed(RenderObject*, const RenderLayer*, RenderLayer::ViewportConstrainedNotCompositedReason*) const;
 
     RenderView& m_renderView;
     CompositingTriggerFlags m_compositingTriggers;

third_party/WebKit/Source/core/rendering/compositing/RenderLayerCompositor.cpp

@@ -466,7 +466,7 @@ bool RenderLayerCompositor::allocateOrClearCompositedLayerMapping(RenderLayer* l
 bool RenderLayerCompositor::updateLayerIfViewportConstrained(RenderLayer* layer)
 {
     RenderLayer::ViewportConstrainedNotCompositedReason viewportConstrainedNotCompositedReason = RenderLayer::NoNotCompositedReason;
-    m_compositingReasonFinder.requiresCompositingForPosition(layer->renderer(), layer, &viewportConstrainedNotCompositedReason);
+    m_compositingReasonFinder.requiresCompositingForPositionFixed(layer->renderer(), layer, &viewportConstrainedNotCompositedReason);
 
     if (layer->viewportConstrainedNotCompositedReason() != viewportConstrainedNotCompositedReason) {
         ASSERT(viewportConstrainedNotCompositedReason == RenderLayer::NoNotCompositedReason || layer->renderer()->style()->position() == FixedPosition);

third_party/WebKit/Source/platform/graphics/CompositingReasons.h

@@ -24,7 +24,7 @@ const uint64_t CompositingReasonActiveAnimation                        = UINT64_
 const uint64_t CompositingReasonTransitionProperty                     = UINT64_C(1) << 7;
 const uint64_t CompositingReasonFilters                                = UINT64_C(1) << 8;
 const uint64_t CompositingReasonPositionFixed                          = UINT64_C(1) << 9;
-const uint64_t CompositingReasonPositionSticky                         = UINT64_C(1) << 10;
+// Bit 10 is available.
 const uint64_t CompositingReasonOverflowScrollingTouch                 = UINT64_C(1) << 11;
 const uint64_t CompositingReasonOverflowScrollingParent                = UINT64_C(1) << 12;
 const uint64_t CompositingReasonOutOfFlowClipping                      = UINT64_C(1) << 13;
@@ -83,7 +83,6 @@ const uint64_t CompositingReasonComboAllDirectReasons =
     | CompositingReasonTransitionProperty
     | CompositingReasonFilters
     | CompositingReasonPositionFixed
-    | CompositingReasonPositionSticky
     | CompositingReasonOverflowScrollingTouch
     | CompositingReasonOverflowScrollingParent
     | CompositingReasonOutOfFlowClipping
@@ -173,9 +172,7 @@ static const CompositingReasonStringMap compositingReasonStringMap[] = {
     { CompositingReasonPositionFixed,
         "positionFixed",
         "Is fixed position" },
-    { CompositingReasonPositionSticky,
-        "positionSticky",
-        "Is sticky position" },
+    { 0, 0, 0 }, // Available.
     { CompositingReasonOverflowScrollingTouch,
         "overflowScrollingTouch",
         "Is a scrollable overflow element" },