Bug 1415225 - Stop setting the EventRegionsOverride flag on in-process subdocument layers. r=botond

The mechanics of this change is fairly straightforward - instead of setting the
override on the layer corresponding to the in-process subdocument, we just set
the flag on the display list builder; that flag is already checked when building
the layer event regions for descendant nsIFrames.

As a side-effect, we also don't need to force a layer for in-process subdocuments
just because they have document-level APZ-aware listeners. One of reasons we were
doing so before was so that we would have a layer to stash the override flags on
but now we don't need that any more.

Note that out-of-process subdocuments are not affected; for those cases
the nsSubDocumentFrame delegates BuildDisplayList to
RenderFrameParent/nsDisplayRemote, which will still set the overrides on
the RefLayer that is created.

MozReview-Commit-ID: GTy9BmVVZ9q

--HG--
extra : rebase_source : be321091d6b5fe4b66738f2deeffbcfa6af0b521

layout/generic/nsSubDocumentFrame.cpp

@@ -447,12 +447,6 @@ nsSubDocumentFrame::BuildDisplayList(nsDisplayListBuilder*   aBuilder,
     needsOwnLayer = true;
   }
 
-  if (!needsOwnLayer && aBuilder->IsBuildingLayerEventRegions() &&
-      nsLayoutUtils::HasDocumentLevelListenersForApzAwareEvents(presShell))
-  {
-    needsOwnLayer = true;
-  }
-
   if (aBuilder->IsRetainingDisplayList()) {
     // The value of needsOwnLayer can change between builds without
     // an invalidation recorded for this frame (like if the root
@@ -505,7 +499,11 @@ nsSubDocumentFrame::BuildDisplayList(nsDisplayListBuilder*   aBuilder,
               ? nsLayoutUtils::FindOrCreateIDFor(rootScrollFrame->GetContent())
               : aBuilder->GetCurrentScrollParentId());
 
-      aBuilder->SetAncestorHasApzAwareEventHandler(false);
+      bool hasDocumentLevelListenersForApzAwareEvents =
+          aBuilder->IsBuildingLayerEventRegions() &&
+          nsLayoutUtils::HasDocumentLevelListenersForApzAwareEvents(presShell);
+
+      aBuilder->SetAncestorHasApzAwareEventHandler(hasDocumentLevelListenersForApzAwareEvents);
       subdocRootFrame->
         BuildDisplayListForStackingContext(aBuilder, &childItems);
     }

layout/painting/nsDisplayList.cpp

@@ -6861,9 +6861,6 @@ nsDisplaySubDocument::nsDisplaySubDocument(nsDisplayListBuilder* aBuilder,
     , mSubDocFrame(aSubDocFrame)
 {
   MOZ_COUNT_CTOR(nsDisplaySubDocument);
-  mForceDispatchToContentRegion =
-    aBuilder->IsBuildingLayerEventRegions() &&
-    nsLayoutUtils::HasDocumentLevelListenersForApzAwareEvents(aFrame->PresContext()->PresShell());
 
   // The SubDocument display item is conceptually outside the viewport frame,
   // so in cases where the viewport frame is an AGR, the SubDocument's AGR
@@ -6879,17 +6876,6 @@ nsDisplaySubDocument::~nsDisplaySubDocument() {
 }
 #endif
 
-already_AddRefed<Layer>
-nsDisplaySubDocument::BuildLayer(nsDisplayListBuilder* aBuilder,
-                                 LayerManager* aManager,
-                                 const ContainerLayerParameters& aContainerParameters) {
-  RefPtr<Layer> layer = nsDisplayOwnLayer::BuildLayer(aBuilder, aManager, aContainerParameters);
-  layer->AsContainerLayer()->SetEventRegionsOverride(mForceDispatchToContentRegion
-    ? EventRegionsOverride::ForceDispatchToContent
-    : EventRegionsOverride::NoOverride);
-  return layer.forget();
-}
-
 UniquePtr<ScrollMetadata>
 nsDisplaySubDocument::ComputeScrollMetadata(LayerManager* aLayerManager,
                                             const ContainerLayerParameters& aContainerParameters)

layout/painting/nsDisplayList.h

@@ -5111,10 +5111,6 @@ public:
   virtual ~nsDisplaySubDocument();
 #endif
 
-  virtual already_AddRefed<Layer> BuildLayer(nsDisplayListBuilder* aBuilder,
-                                             LayerManager* aManager,
-                                             const ContainerLayerParameters& aContainerParameters) override;
-
   virtual nsRect GetBounds(nsDisplayListBuilder* aBuilder,
                            bool* aSnap) const override;