Initial scroll-blocks-on compositor integration

Source/core/rendering/compositing/CompositedLayerMapping.cpp

Index: Source/core/rendering/compositing/CompositedLayerMapping.cpp
diff --git a/Source/core/rendering/compositing/CompositedLayerMapping.cpp b/Source/core/rendering/compositing/CompositedLayerMapping.cpp
index ccd7e6e7b138b5529efe4faef748dc126c5a7f31..d3191f074678258d3e04db956e480a157b3d4016 100644
--- a/Source/core/rendering/compositing/CompositedLayerMapping.cpp
+++ b/Source/core/rendering/compositing/CompositedLayerMapping.cpp
@@ -236,6 +236,8 @@ void CompositedLayerMapping::createPrimaryGraphicsLayer()
         updateLayerBlendMode(renderer()->style());
         updateIsRootForIsolatedGroup();
     }
+
+    updateScrollBlocksOn(renderer()->style());
 }
 
 void CompositedLayerMapping::destroyGraphicsLayers()
@@ -295,6 +297,18 @@ void CompositedLayerMapping::updateIsRootForIsolatedGroup()
     m_graphicsLayer->setIsRootForIsolatedGroup(isolate);
 }
 
+void CompositedLayerMapping::updateScrollBlocksOn(const RenderStyle* style)
+{
+    // Note that blink determines the default scroll blocking policy, even
+    // when the scroll-blocks-on CSS feature isn't enabled.
+    WebScrollBlocksOn blockingMode = WebScrollBlocksOnStartTouch | WebScrollBlocksOnWheelEvent;
+
+    if (RuntimeEnabledFeatures::cssScrollBlocksOnEnabled())
+        blockingMode = style->scrollBlocksOn();
+
+    m_graphicsLayer->setScrollBlocksOn(blockingMode);
+}
+
 void CompositedLayerMapping::updateContentsOpaque()
 {
     ASSERT(m_isMainFrameRenderViewLayer || !m_backgroundLayer);
@@ -715,6 +729,8 @@ void CompositedLayerMapping::updateGraphicsLayerGeometry(const RenderLayer* comp
     updateScrollParent(compositor()->preferCompositingToLCDTextEnabled() ? m_owningLayer.scrollParent() : 0);
     registerScrollingLayers();
 
+    updateScrollBlocksOn(renderer()->style());
+
     updateCompositingReasons();
 }