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 af5e44b63a02f65b54035a8366e6f7441c24f36f..c6c0d46228206752252ade6f90b50f6cf6a70853 100644
--- a/Source/web/WebViewImpl.cpp
+++ b/Source/web/WebViewImpl.cpp
@@ -3633,6 +3633,12 @@ 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();
 
@@ -3687,7 +3693,7 @@ void WebViewImpl::setRootGraphicsLayer(GraphicsLayer* layer)
         if (layer) {
             m_rootGraphicsLayer = pinchViewport.rootGraphicsLayer();
             m_rootLayer = pinchViewport.rootGraphicsLayer()->platformLayer();
-            m_rootTransformLayer = 0;
+            m_rootTransformLayer = pinchViewport.rootGraphicsLayer();
         } else {
             m_rootGraphicsLayer = 0;
             m_rootLayer = 0;
@@ -3941,6 +3947,8 @@ 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();