Separate VisualViewport layer tree creation from attachment.

third_party/WebKit/Source/core/layout/compositing/PaintLayerCompositor.cpp

Index: third_party/WebKit/Source/core/layout/compositing/PaintLayerCompositor.cpp
diff --git a/third_party/WebKit/Source/core/layout/compositing/PaintLayerCompositor.cpp b/third_party/WebKit/Source/core/layout/compositing/PaintLayerCompositor.cpp
index b80b4bacc2b14934db7a6f20c78d15a570706e3b..960e797a567a0e278c8e0bfb066efd0e17373b59 100644
--- a/third_party/WebKit/Source/core/layout/compositing/PaintLayerCompositor.cpp
+++ b/third_party/WebKit/Source/core/layout/compositing/PaintLayerCompositor.cpp
@@ -462,7 +462,7 @@ void PaintLayerCompositor::updateIfNeeded() {
   }
 
   // Inform the inspector that the layer tree has changed.
-  if (m_layoutView.frame()->isMainFrame())
+  if (isMainFrame())
     probe::layerTreeDidChange(m_layoutView.frame());
 }
 
@@ -723,7 +723,7 @@ std::unique_ptr<JSONObject> PaintLayerCompositor::layerTreeAsJSON(
   // root.
   GraphicsLayer* rootLayer = m_rootContentLayer.get();
   if (flags & LayerTreeIncludesRootLayer) {
-    if (m_layoutView.frame()->isMainFrame()) {
+    if (isMainFrame()) {
       while (rootLayer->parent())
         rootLayer = rootLayer->parent();
     } else {
@@ -1046,11 +1046,8 @@ void PaintLayerCompositor::updateOverflowControlsLayers() {
   // Main frame scrollbars should always be stuck to the sides of the screen (in
   // overscroll and in pinch-zoom), so make the parent for the scrollbars be the
   // viewport container layer.
-  if (m_layoutView.frame()->isMainFrame()) {
-    VisualViewport& visualViewport =
-        m_layoutView.frameView()->page()->frameHost().visualViewport();
-    controlsParent = visualViewport.containerLayer();
-  }
+  if (isMainFrame())
+    controlsParent = visualViewport().containerLayer();
 
   if (requiresHorizontalScrollbarLayer()) {
     if (!m_layerForHorizontalScrollbar) {
@@ -1119,6 +1116,9 @@ void PaintLayerCompositor::ensureRootLayer() {
   if (expectedAttachment == m_rootLayerAttachment)
     return;
 
+  if (isMainFrame())
+    visualViewport().createLayerTree();
+
   if (!m_rootContentLayer) {
     m_rootContentLayer = GraphicsLayer::create(this);
     IntRect overflowRect = m_layoutView.pixelSnappedLayoutOverflowRect();
@@ -1330,6 +1330,14 @@ DocumentLifecycle& PaintLayerCompositor::lifecycle() const {
   return m_layoutView.document().lifecycle();
 }
 
+bool PaintLayerCompositor::isMainFrame() const {
+  return m_layoutView.frame()->isMainFrame();
+}
+
+VisualViewport& PaintLayerCompositor::visualViewport() const {
+  return m_layoutView.frameView()->page()->frameHost().visualViewport();
+}
+
 String PaintLayerCompositor::debugName(
     const GraphicsLayer* graphicsLayer) const {
   String name;