Move dragThreshold definition to util/

In order to avoid multiple declarations that has to be updated in the
case of future updates.

core/rfb.js

@@ -12,6 +12,7 @@
 
 import * as Log from './util/logging.js';
 import { decodeUTF8 } from './util/strings.js';
+import { dragThreshold } from './util/browser.js';
 import EventTargetMixin from './util/eventtarget.js';
 import Display from "./display.js";
 import Keyboard from "./input/keyboard.js";
@@ -785,10 +786,6 @@ export default class RFB extends EventTargetMixin {
             const deltaX = this._viewportDragPos.x - x;
             const deltaY = this._viewportDragPos.y - y;
 
-            // The goal is to trigger on a certain physical width, the
-            // devicePixelRatio brings us a bit closer but is not optimal.
-            const dragThreshold = 10 * (window.devicePixelRatio || 1);
-
             if (this._viewportHasMoved || (Math.abs(deltaX) > dragThreshold ||
                                            Math.abs(deltaY) > dragThreshold)) {
                 this._viewportHasMoved = true;

core/util/browser.js

@@ -1,6 +1,7 @@
 /*
  * noVNC: HTML5 VNC client
  * Copyright (C) 2012 Joel Martin
+ * Copyright (C) 2018 Samuel Mannehed for Cendio AB
  * Licensed under MPL 2.0 (see LICENSE.txt)
  *
  * See README.md for usage and integration instructions.
@@ -20,6 +21,11 @@ window.addEventListener('touchstart', function onFirstTouch() {
     window.removeEventListener('touchstart', onFirstTouch, false);
 }, false);
 
+
+// The goal is to find a certain physical width, the devicePixelRatio
+// brings us a bit closer but is not optimal.
+export let dragThreshold = 10 * (window.devicePixelRatio || 1);
+
 let _cursor_uris_supported = null;
 
 export function supportsCursorURIs () {