Defer ChromeClient::attachRootGraphicsLayer until after compositing update.

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 960e797a567a0e278c8e0bfb066efd0e17373b59..aa5ef52254f60256d7d8963d211e8db862c0cab8 100644
--- a/third_party/WebKit/Source/core/layout/compositing/PaintLayerCompositor.cpp
+++ b/third_party/WebKit/Source/core/layout/compositing/PaintLayerCompositor.cpp
@@ -83,7 +83,8 @@ PaintLayerCompositor::PaintLayerCompositor(LayoutView& layoutView)
       m_isTrackingRasterInvalidations(
           layoutView.frameView()->isTrackingPaintInvalidations()),
       m_inOverlayFullscreenVideo(false),
-      m_rootLayerAttachment(RootLayerUnattached) {
+      m_rootLayerAttachment(RootLayerUnattached),
+      m_pendingChromeClientAttachment(false) {
   updateAcceleratedCompositingSettings();
 }
 
@@ -461,6 +462,14 @@ void PaintLayerCompositor::updateIfNeeded() {
         layersNeedingPaintInvalidation[i]->layoutObject());
   }
 
+  if (m_pendingChromeClientAttachment) {
+    if (Page* page = m_layoutView.frame()->page()) {
+      page->chromeClient().attachRootGraphicsLayer(rootGraphicsLayer(),
+                                                   m_layoutView.frame());
+      m_pendingChromeClientAttachment = false;
+    }
+  }
+
   // Inform the inspector that the layer tree has changed.
   if (isMainFrame())
     probe::layerTreeDidChange(m_layoutView.frame());
@@ -1228,14 +1237,9 @@ void PaintLayerCompositor::attachRootLayer(RootLayerAttachment attachment) {
     case RootLayerUnattached:
       ASSERT_NOT_REACHED();
       break;
-    case RootLayerAttachedViaChromeClient: {
-      LocalFrame& frame = m_layoutView.frameView()->frame();
-      Page* page = frame.page();
-      if (!page)
-        return;
-      page->chromeClient().attachRootGraphicsLayer(rootGraphicsLayer(), &frame);
+    case RootLayerAttachedViaChromeClient:
+      m_pendingChromeClientAttachment = true;

[szager1, 2017/03/06 22:23:34]

Is this new variable necessary?  Can't you just call attachRootLayer only from
updateIfNeeded?

[skobes, 2017/03/06 22:44:23]

Not easily - attachRootLayer updates m_rootLayerAttachment, and in the iframe
case it calls setNeedsCompositingUpdate.  Those things should happen immediately
and not be deferred.

[szager1, 2017/03/06 22:57:58]

Could you add a RootLayerPendingAttachment value to the RootLayerAttachment
enum?  It looks like, aside from attachRootLayer(), the only places in the code
that look at m_rootLayerAttachment are only interested in whether or not it's
RootLayerUnattached.

[skobes, 2017/03/07 23:05:46]

Done, PTAL.

       break;
-    }
     case RootLayerAttachedViaEnclosingFrame: {
       HTMLFrameOwnerElement* ownerElement =
           m_layoutView.document().localOwner();
@@ -1283,6 +1287,7 @@ void PaintLayerCompositor::detachRootLayer() {
   }
 
   m_rootLayerAttachment = RootLayerUnattached;
+  m_pendingChromeClientAttachment = false;
 }
 
 void PaintLayerCompositor::updateRootLayerAttachment() {