Implement will-change-based creation of layers, stacking contexts, and containing blocks

Source/core/rendering/style/RenderStyle.cpp

Index: Source/core/rendering/style/RenderStyle.cpp
diff --git a/Source/core/rendering/style/RenderStyle.cpp b/Source/core/rendering/style/RenderStyle.cpp
index dd038901323beff4ea13f628e031ea0377bd54aa..75558d6645ce33b6fce395b5cdfca14d44e878f5 100644
--- a/Source/core/rendering/style/RenderStyle.cpp
+++ b/Source/core/rendering/style/RenderStyle.cpp
@@ -650,7 +650,8 @@ StyleDifference RenderStyle::repaintOnlyDiff(const RenderStyle* other, unsigned&
             || rareNonInheritedData->m_backfaceVisibility != other->rareNonInheritedData->m_backfaceVisibility
             || rareNonInheritedData->m_perspective != other->rareNonInheritedData->m_perspective
             || rareNonInheritedData->m_perspectiveOriginX != other->rareNonInheritedData->m_perspectiveOriginX
-            || rareNonInheritedData->m_perspectiveOriginY != other->rareNonInheritedData->m_perspectiveOriginY)
+            || rareNonInheritedData->m_perspectiveOriginY != other->rareNonInheritedData->m_perspectiveOriginY
+            || hasWillChangeCompositingHint() != other->hasWillChangeCompositingHint())
             return StyleDifferenceRecompositeLayer;
     }
 
@@ -831,6 +832,25 @@ bool RenderStyle::hasIsolation() const
     return false;
 }
 
+bool RenderStyle::hasWillChangeCompositingHint() const
+{
+    for (size_t i = 0; i < rareNonInheritedData->m_willChange->m_properties.size(); ++i) {
+        switch (rareNonInheritedData->m_willChange->m_properties[i]) {
+        case CSSPropertyOpacity:
+        case CSSPropertyWebkitTransform:
+        case CSSPropertyLeft:
+        case CSSPropertyTop:
+        case CSSPropertyRight:
+        case CSSPropertyBottom:
+        case CSSPropertyWebkitFilter:
+            return true;
+        default:
+            break;
+        }
+    }
+    return false;
+}
+
 inline bool requireTransformOrigin(const Vector<RefPtr<TransformOperation> >& transformOperations, RenderStyle::ApplyTransformOrigin applyOrigin)
 {
     // transform-origin brackets the transform with translate operations.