Simplify selectionCollapsed, move to dom.js

FIX: Fixes reading of selection in Chrome in a shadow DOM.

src/dom.js

@@ -1,3 +1,5 @@
+const browser = require("./browser")
+
 const domIndex = exports.domIndex = function(node) {
   for (var index = 0;; index++) {
     node = node.previousSibling
@@ -50,3 +52,12 @@ function hasBlockDesc(dom) {
   let desc = dom.pmViewDesc
   return desc && desc.node && desc.node.isBlock
 }
+
+// Work around Chrome issue https://bugs.chromium.org/p/chromium/issues/detail?id=447523
+// (isCollapsed inappropriately returns true in shadow dom)
+exports.selectionCollapsed = function(domSel) {
+  let collapsed = domSel.isCollapsed
+  if (collapsed && browser.chrome && domSel.rangeCount && !domSel.getRangeAt(0).collapsed)
+    collapsed = false
+  return collapsed
+}

src/domchange.js

@@ -3,7 +3,8 @@ const {Selection} = require("prosemirror-state")
 const {Mapping} = require("prosemirror-transform")
 
 const {TrackMappings} = require("./trackmappings")
-const {selectionBetween, selectionCollapsed} = require("./selection")
+const {selectionBetween} = require("./selection")
+const {selectionCollapsed} = require("./dom")
 
 class DOMChange {
   constructor(view, composing) {

src/selection.js

@@ -1,6 +1,7 @@
 const {TextSelection, NodeSelection} = require("prosemirror-state")
 
 const browser = require("./browser")
+const {selectionCollapsed} = require("./dom")
 
 // Track the state of the current editor selection. Keeps the editor
 // selection in sync with the DOM selection by polling for changes,
@@ -220,21 +221,6 @@ function temporarilyEditable(view, pos) {
   }
 }
 
-function selectionCollapsed(selection) {
-  if (!selection.isCollapsed) {
-    return false
-  }
-
-  for (let i = 0, k = selection.rangeCount; i < k; i++) {
-    if (!selection.getRangeAt(i).collapsed) {
-      return false
-    }
-  }
-
-  return true
-}
-exports.selectionCollapsed = selectionCollapsed
-
 function removeClassOnSelectionChange(view) {
   document.removeEventListener("selectionchange", view.hideSelectionGuard)
   let domSel = view.root.getSelection()