Suppress layer creation for descendants of GPU-rasterized layers

Source/core/rendering/compositing/CompositingRequirementsUpdater.cpp

Index: Source/core/rendering/compositing/CompositingRequirementsUpdater.cpp
diff --git a/Source/core/rendering/compositing/CompositingRequirementsUpdater.cpp b/Source/core/rendering/compositing/CompositingRequirementsUpdater.cpp
index cb11a721f59b49073306b59b5ea4be623bd6f3a5..146c399aeccd3bd9518d2c469381aa75ec9bed74 100644
--- a/Source/core/rendering/compositing/CompositingRequirementsUpdater.cpp
+++ b/Source/core/rendering/compositing/CompositingRequirementsUpdater.cpp
@@ -163,6 +163,7 @@ public:
         , m_subtreeIsCompositing(false)
         , m_hasUnisolatedCompositedBlendingDescendant(false)
         , m_testingOverlap(testOverlap)
+        , m_suppressLayerCreation(false)
 #ifndef NDEBUG
         , m_depth(0)
 #endif
@@ -175,6 +176,7 @@ public:
         , m_subtreeIsCompositing(other.m_subtreeIsCompositing)
         , m_hasUnisolatedCompositedBlendingDescendant(other.m_hasUnisolatedCompositedBlendingDescendant)
         , m_testingOverlap(other.m_testingOverlap)
+        , m_suppressLayerCreation(other.m_suppressLayerCreation)
 #ifndef NDEBUG
         , m_depth(other.m_depth + 1)
 #endif
@@ -186,6 +188,7 @@ public:
     bool m_subtreeIsCompositing;
     bool m_hasUnisolatedCompositedBlendingDescendant;
     bool m_testingOverlap;
+    bool m_suppressLayerCreation;
 #ifndef NDEBUG
     int m_depth;
 #endif
@@ -201,6 +204,11 @@ static bool requiresCompositingOrSquashing(CompositingReasons reasons)
     return reasons != CompositingReasonNone;
 }
 
+static bool shouldMakeDescendantsSuppressCompositedLayerCreation(CompositingReasons reasons)
+{
+    return reasons & CompositingReasonWillChangeGpuRasterizationHint;
+}
+
 static CompositingReasons subtreeReasonsForCompositing(RenderObject* renderer, bool hasCompositedDescendants, bool has3DTransformedDescendants)
 {
     CompositingReasons subtreeReasons = CompositingReasonNone;
@@ -294,6 +302,9 @@ void CompositingRequirementsUpdater::updateRecursive(RenderLayer* ancestorLayer,
 
     // First accumulate the straightforward compositing reasons.
     CompositingReasons directReasons = m_compositingReasonFinder.directReasons(layer, m_needsToRecomputeCompositingRequirements);
+    layer->setSuppressingCompositedLayerCreation(currentRecursionData.m_suppressLayerCreation);
+    if (layer->suppressingCompositedLayerCreation())
+        directReasons = m_compositingReasonFinder.suppressWillChangeAndAnimationForGpuRasterization(layer, directReasons);
 
     // Video is special. It's the only RenderLayer type that can both have
     // RenderLayer children and whose children can't use its backing to render
@@ -348,6 +359,7 @@ void CompositingRequirementsUpdater::updateRecursive(RenderLayer* ancestorLayer,
     // ancestor with m_subtreeIsCompositing set to false.
     RecursionData childRecursionData(currentRecursionData);
     childRecursionData.m_subtreeIsCompositing = false;
+    childRecursionData.m_suppressLayerCreation = layer->suppressingCompositedLayerCreation() || shouldMakeDescendantsSuppressCompositedLayerCreation(directReasons);
 
     bool willBeCompositedOrSquashed = compositor->canBeComposited(layer) && requiresCompositingOrSquashing(reasonsToComposite);
     if (willBeCompositedOrSquashed) {