Paint local attachment backgrounds into composited scrolling contents layer

third_party/WebKit/Source/core/style/ComputedStyle.cpp

Index: third_party/WebKit/Source/core/style/ComputedStyle.cpp
diff --git a/third_party/WebKit/Source/core/style/ComputedStyle.cpp b/third_party/WebKit/Source/core/style/ComputedStyle.cpp
index 984ff42be192101a07c21c53955cd3c42a23b460..4d8f7ef63fb2faf02ec3aa710df4e9ff217965d4 100644
--- a/third_party/WebKit/Source/core/style/ComputedStyle.cpp
+++ b/third_party/WebKit/Source/core/style/ComputedStyle.cpp
@@ -1205,6 +1205,21 @@ bool ComputedStyle::hasEntirelyFixedBackground() const
     return allLayersAreFixed(backgroundLayers());
 }
 
+static bool allLayersAreLocal(const FillLayer& layer)
+{
+    for (const FillLayer* currLayer = &layer; currLayer; currLayer = currLayer->next()) {
+        if (currLayer->attachment() != LocalBackgroundAttachment)
+            return false;
+    }
+
+    return true;
+}
+
+bool ComputedStyle::hasEntirelyLocalBackground() const
+{
+    return allLayersAreLocal(backgroundLayers());
+}
+
 const CounterDirectiveMap* ComputedStyle::counterDirectives() const
 {
     return m_rareNonInheritedData->m_counterDirectives.get();