Made root translation layer the root when using pinch virtual viewport.

Source/web/WebViewImpl.cpp

Index: Source/web/WebViewImpl.cpp
diff --git a/Source/web/WebViewImpl.cpp b/Source/web/WebViewImpl.cpp
index 050bd2730cd8252e35298b00cfc689c840c95d8a..e54f2b7c2cd1558f864d17e50ccb18203db7e1b4 100644
--- a/Source/web/WebViewImpl.cpp
+++ b/Source/web/WebViewImpl.cpp
@@ -3638,6 +3638,12 @@ void WebViewImpl::setOverlayLayer(WebCore::GraphicsLayer* layer)
     if (!m_rootGraphicsLayer)
         return;
 
+    if (pinchVirtualViewportEnabled()) {
+        m_page->mainFrame()->view()->renderView()->compositor()->setOverlayLayer(layer);
+        return;
+    }
+
+    // FIXME(bokan): This path goes away after virtual viewport pinch is enabled everywhere.
     if (!m_rootTransformLayer)
         m_rootTransformLayer = m_page->mainFrame()->view()->renderView()->compositor()->ensureRootTransformLayer();
 
@@ -3692,7 +3698,7 @@ void WebViewImpl::setRootGraphicsLayer(GraphicsLayer* layer)
         if (layer) {
             m_rootGraphicsLayer = pinchViewport.rootGraphicsLayer();
             m_rootLayer = pinchViewport.rootGraphicsLayer()->platformLayer();
-            m_rootTransformLayer = 0;
+            m_rootTransformLayer = pinchViewport.rootTransformLayer();
         } else {
             m_rootGraphicsLayer = 0;
             m_rootLayer = 0;
@@ -3946,6 +3952,8 @@ void WebViewImpl::updateRootLayerTransform()
     if (!m_rootGraphicsLayer)
         return;
 
+    // FIXME(bokan): m_rootTransformLayer is always set here in pinch virtual viewport. This can go away once
+    // that's default everywhere.
     if (!m_rootTransformLayer)
         m_rootTransformLayer = m_page->mainFrame()->view()->renderView()->compositor()->ensureRootTransformLayer();