Plumb selection bounds as a single unit

public/platform/WebLayerTreeView.h

Index: public/platform/WebLayerTreeView.h
diff --git a/public/platform/WebLayerTreeView.h b/public/platform/WebLayerTreeView.h
index bcc5f1e858d19d0aecc2c98df715b938dc137bec..ccfea5f2aab9de545a387b1a9ae5ecf7fb52cf6c 100644
--- a/public/platform/WebLayerTreeView.h
+++ b/public/platform/WebLayerTreeView.h
@@ -42,6 +42,7 @@ class WebCompositeAndReadbackAsyncCallback;
 class WebLayer;
 struct WebPoint;
 struct WebSelectionBound;
+class WebSelection;
 class WebWidget;
 
 class WebLayerTreeView {
@@ -130,10 +131,9 @@ public:
     virtual void clearViewportLayers() { }
 
     // Used to update the active selection bounds.
-    // If the (empty) selection is an insertion point, |start| and |end| will be identical with type |Caret|.
-    // If the (non-empty) selection has mixed RTL/LTR text, |start| and |end| may share the same type,
-    // |SelectionLeft| or |SelectionRight|.
+    // FIXME: Remove this overload when downstream consumers have been updated to use WebSelection, crbug.com/466672.
     virtual void registerSelection(const WebSelectionBound& start, const WebSelectionBound& end) { }
+    virtual void registerSelection(const WebSelection&) { }
     virtual void clearSelection() { }
 
     // Debugging / dangerous ---------------------------------------------