Fix #1203: Selection: Make Edge ignore user-select

Edge fools feature detection by populating both msUserSelect and
WebkitUserSelect.  This change forces Edge down the same code path as IE,
and removes redundant code that is already present in all versions of
Dojo that dgrid supports now.

(cherry picked from commit 7211f6d)

README.md

@@ -48,7 +48,7 @@ Alternatively, dgrid and its dependencies can be downloaded individually:
 * [xstyle](https://github.com/kriszyp/xstyle)
 * [put-selector](https://github.com/kriszyp/put-selector)
 * [dstore](https://github.com/SitePen/dstore) for store-backed grids
-* [The Dojo Toolkit](http://dojotoolkit.org) SDK version 1.8 or higher
+* [The Dojo Toolkit](http://dojotoolkit.org) SDK version 1.8.2 or higher
     * Out of the DTK components, Dojo core is the only hard dependency for dgrid;
       however, some of the test pages also use components from Dijit, and
       Dojox (namely grid for a comparison test, and mobile for a mobile page).
@@ -91,7 +91,7 @@ packages: [
 
 # Browser and Dojo Version Support
 
-dgrid 0.4 works with Dojo 1.8 or higher, and supports the following browsers:
+dgrid 0.4 works with Dojo 1.8.2 or higher, and supports the following browsers:
 
 * IE 8+
 * Firefox latest + ESR

Selection.js

@@ -7,35 +7,15 @@ define([
 	'dojo/has!touch?./util/touch',
 	'put-selector/put',
 	'dojo/query',
-	'dojo/_base/sniff'
+	'dojo/_base/sniff',
+	'dojo/dom' // for has('css-user-select') in 1.8.2+
 ], function (declare, on, has, aspect, List, touchUtil, put) {
 
 	has.add('dom-comparedocumentposition', function (global, doc, element) {
 		return !!element.compareDocumentPosition;
 	});
 
-	// Add feature test for user-select CSS property for optionally disabling
-	// text selection.
-	// (Can't use dom.setSelectable prior to 1.8.2 because of bad sniffs, see #15990)
-	has.add('css-user-select', function (global, doc, element) {
-		var style = element.style,
-			prefixes = ['Khtml', 'O', 'ms', 'Moz', 'Webkit'],
-			i = prefixes.length,
-			name = 'userSelect';
-
-		// Iterate prefixes from most to least likely
-		do {
-			if (typeof style[name] !== 'undefined') {
-				// Supported; return property name
-				return name;
-			}
-		} while (i-- && (name = prefixes[i] + 'UserSelect'));
-
-		// Not supported if we didn't return before now
-		return false;
-	});
-
-	// Also add a feature test for the onselectstart event, which offers a more
+	// Add a feature test for the onselectstart event, which offers a more
 	// graceful fallback solution than node.unselectable.
 	has.add('dom-selectstart', typeof document.onselectstart !== 'undefined');
 
@@ -46,6 +26,11 @@ define([
 		downType = hasPointer ? hasPointer + (hasMSPointer ? 'Down' : 'down') : 'mousedown',
 		upType = hasPointer ? hasPointer + (hasMSPointer ? 'Up' : 'up') : 'mouseup';
 
+	if (hasUserSelect === 'WebkitUserSelect' && typeof document.documentElement.style.msUserSelect !== 'undefined') {
+		// Edge defines both webkit and ms prefixes, rendering feature detects as brittle as UA sniffs...
+		hasUserSelect = false;
+	}
+
 	function makeUnselectable(node, unselectable) {
 		// Utility function used in fallback path for recursively setting unselectable
 		var value = node.unselectable = unselectable ? 'on' : '',
@@ -74,6 +59,7 @@ define([
 		// When using a modifier key, IE will select text inside of the element as well
 		// as outside of the element, because it thinks the selection started outside.
 		// Therefore, fall back to other means of blocking selection for IE10+.
+		// Newer versions of Dojo do not even report msUserSelect (see https://github.com/dojo/dojo/commit/7ae2a43).
 		if (hasUserSelect && hasUserSelect !== 'msUserSelect') {
 			node.style[hasUserSelect] = value;
 		}