Suppress layer creation for descendants of GPU-rasterized layers

Source/core/rendering/compositing/CompositingReasonFinder.cpp

Index: Source/core/rendering/compositing/CompositingReasonFinder.cpp
diff --git a/Source/core/rendering/compositing/CompositingReasonFinder.cpp b/Source/core/rendering/compositing/CompositingReasonFinder.cpp
index e7a901c1f216022525455093badd09039a449013..2146b468c7636428853d160c4c519a79038c26f3 100644
--- a/Source/core/rendering/compositing/CompositingReasonFinder.cpp
+++ b/Source/core/rendering/compositing/CompositingReasonFinder.cpp
@@ -89,10 +89,24 @@ bool CompositingReasonFinder::isMainFrame() const
     return !m_renderView.document().ownerElement();
 }
 
+CompositingReasons CompositingReasonFinder::suppressStyleDeterminedReasonsIfPossible(const RenderLayer* layer, CompositingReasons styleReasons) const
+{
+    CompositingReasons adjustedReasons = styleReasons;
+    adjustedReasons &= ~(CompositingReasonWillChangeCompositingHint | CompositingReasonWillChangeGpuRasterizationHint);
+
+    // We can suppress layer creation for animations before animations start, but not
+    // once they're already running on the compositor.
+    if (!layer->renderer()->style()->isRunningAnimationOnCompositor())
+        adjustedReasons &= ~CompositingReasonActiveAnimation;
+
+    return adjustedReasons;
+}
+
+
 CompositingReasons CompositingReasonFinder::directReasons(const RenderLayer* layer, bool* needToRecomputeCompositingRequirements) const
 {
     CompositingReasons styleReasons = layer->styleDeterminedCompositingReasons();
-    ASSERT(styleDeterminedReasons(layer->renderer()) == styleReasons);
+    ASSERT(styleDeterminedReasons(layer) == styleReasons);
     return styleReasons | nonStyleDeterminedDirectReasons(layer, needToRecomputeCompositingRequirements);
 }
 
@@ -111,9 +125,10 @@ bool CompositingReasonFinder::requiresCompositingForScrollableFrame() const
     return frameView->isScrollable();
 }
 
-CompositingReasons CompositingReasonFinder::styleDeterminedReasons(RenderObject* renderer) const
+CompositingReasons CompositingReasonFinder::styleDeterminedReasons(const RenderLayer* layer) const
 {
     CompositingReasons directReasons = CompositingReasonNone;
+    RenderObject* renderer = layer->renderer();
 
     if (requiresCompositingForTransform(renderer))
         directReasons |= CompositingReason3DTransform;
@@ -127,8 +142,14 @@ CompositingReasons CompositingReasonFinder::styleDeterminedReasons(RenderObject*
     if (requiresCompositingForFilters(renderer))
         directReasons |= CompositingReasonFilters;
 
-    if (requiresCompositingForWillChange(renderer))
-        directReasons |= CompositingReasonWillChange;
+    if (requiresCompositingForWillChangeCompositingHint(renderer))
+        directReasons |= CompositingReasonWillChangeCompositingHint;
+
+    if (requiresCompositingForWillChangeGpuRasterizationHint(renderer))
+        directReasons |= CompositingReasonWillChangeGpuRasterizationHint;
+
+    if (layer->suppressingCompositedLayerCreation())
+        directReasons = suppressStyleDeterminedReasonsIfPossible(layer, directReasons);
 
     ASSERT(!(directReasons & ~CompositingReasonComboAllStyleDeterminedReasons));
     return directReasons;
@@ -160,11 +181,13 @@ bool CompositingReasonFinder::requiresCompositingForFilters(RenderObject* render
     return renderer->hasFilter();
 }
 
-bool CompositingReasonFinder::requiresCompositingForWillChange(const RenderObject* renderer) const
+bool CompositingReasonFinder::requiresCompositingForWillChangeCompositingHint(const RenderObject* renderer) const
 {
-    if (renderer->style()->hasWillChangeCompositingHint())
-        return true;
+    return renderer->style()->hasWillChangeCompositingHint();
+}
 
+bool CompositingReasonFinder::requiresCompositingForWillChangeGpuRasterizationHint(const RenderObject* renderer) const
+{
     if (!(m_compositingTriggers & GPURasterizationTrigger))
         return false;