prevent crash on win.showDevTools in normal build flavor

docs/References/Window.md

@@ -297,7 +297,7 @@ Turn the window's native shadow on/off. Useful for frameless, transparent window
     The behavior of the function is changed since 0.13.0. Please see [Migration Notes from 0.12 to 0.13](../For Users/Migration/From 0.12 to 0.13.md).
 
 * `iframe` `{String} or {HTMLIFrameElement}` _Optional_ the id or the element of the `<iframe>` to be jailed on. By default, the DevTools is shown for entire window.
-* `callback(dev_win)` `{Function}` callback with the native window of the DevTools window.
+* `callback(dev_win, error)` `{Function}` callback with the native window of the DevTools window.
 
 Open the devtools to inspect the window.
 
@@ -309,6 +309,14 @@ This function returns a `Window` object via the callback. You can use any proper
 
 See also in [webview reference](webview Tag.md) on how to open DevTools for webview or open DevTools in a webview.
 
+```js
+win.showDevTools((dev_win, error) => {
+    if (error) {
+        // handle error
+    }
+});
+```
+
 ## win.closeDevTools()
 
 !!! note
@@ -320,9 +328,9 @@ Close the devtools window.
 
 Enumerate the printers in the system. The callback function will receive an array of JSON objects for the printer information. The device name of the JSON object can be used as parameter in `nw.Window.print()`.
 
-## win.isDevToolsOpen()
+## win.isDevToolsOpen(callback)
 ```javascript
-nw.Window.isOpenDevTools((status) => console.log(status))
+win.isDevToolsOpen((status) => console.log(status))
 ```
 
 !!! note

src/resources/api_nw_newwin.js

@@ -374,15 +374,35 @@ NWWindow.prototype.toggleKioskMode = function() {
   currentNWWindowInternal.toggleKioskModeInternal(this.cWindow.id);
 };
 
-NWWindow.prototype.showDevTools = function(frm, callback) {
-  var id = '';
-  if (typeof frm === 'string')
-    id = frm;
-  var f = null;
+/**
+ * Open the devtools to inspect the window.
+ * 
+ * @param {string | HTMLIFrameElement} [iframe] The `id` or element of the `<iframe>` to be jailed on. By default, the DevTools is shown for entire window. 
+ * @param {(dev_win: Window, error: Error) => void} callback Callback with the native window of the DevTools window.
+ * @returns {void}
+ */
+NWWindow.prototype.showDevTools = function(iframe, callback) {
+  let error;
+  if (process.versions['nw-flavor'] !== 'sdk') {
+    error = new Error('This API is only available on SDK build flavor. Current build flavor is ' + process.versions['nw-flavor']);
+    callback(undefined, error);
+    return;
+  }
+  if (process.versions['nw-flavor'] === 'sdk') {
+    if (nw.App.argv.includes('--disable-devtools')) {
+      error = new Error('DevTools is disabled by --disable-devtools command line flag.');
+      callback(undefined, error);
+      return;
+    }
+  }
+  let id = '';
+  if (typeof iframe === 'string')
+    id = iframe;
+  let f = null;
   if (id)
     f = this.window.getElementById(id);
   else
-    f = frm || null;
+    f = iframe || null;
   nwNatives.setDevToolsJail(f);
   currentNWWindowInternal.showDevTools2Internal(this.cWindow.id, callback);
 };
@@ -760,11 +780,13 @@ apiBridge.registerCustomHook(function(bindingsAPI) {
       callback(cwindows.map(create_nw_win));
     });
   });
+
   apiFunctions.setHandleRequest('isDevToolsOpen', function(callback) {
     return chrome.windows.getAll({ populate: true, windowTypes: ['devtools'] }, function(wins) {
       callback(wins.length > 0);
     })
   });
+
   apiFunctions.setHandleRequest('open', function(url, params, callback) {
     var options = {'url': url, 'setSelfAsOpener': true, 'type': 'popup'};
     //FIXME: unify this conversion code with nwjs/default.js

src/resources/api_nw_window.js

@@ -378,18 +378,39 @@ apiBridge.registerCustomHook(function(bindingsAPI) {
       currentNWWindowInternal.toggleKioskModeInternal();
     };
 
-    NWWindow.prototype.showDevTools = function(frm, callback) {
-      var id = '';
-      if (typeof frm === 'string')
-        id = frm;
-      var f = null;
+    /**
+    * Open the devtools to inspect the window.
+    * 
+    * @param {string | HTMLIFrameElement} [iframe] The `id` or element of the `<iframe>` to be jailed on. By default, the DevTools is shown for entire window. 
+    * @param {(dev_win: Window, error: Error) => void} callback Callback with the native window of the DevTools window.
+    * @returns {void}
+    */
+    NWWindow.prototype.showDevTools = function(iframe, callback) {
+      let error;
+      if (process.versions['nw-flavor'] !== 'sdk') {
+        error = new Error('This API is only available on SDK build flavor. Current build flavor is ' + process.versions['nw-flavor']);
+        callback(undefined, error);
+        return;
+      }
+      if (process.versions['nw-flavor'] === 'sdk') {
+        if (nw.App.argv.includes('--disable-devtools')) {
+          error = new Error('DevTools is disabled by --disable-devtools command line flag.');
+          callback(undefined, error);
+          return;
+        }
+      }
+      let id = '';
+      if (typeof iframe === 'string')
+        id = iframe;
+      let f = null;
       if (id)
         f = this.appWindow.contentWindow.getElementById(id);
       else
-        f = frm || null;
+        f = iframe || null;
       nwNatives.setDevToolsJail(f);
       currentNWWindowInternal.showDevToolsInternal(callback);
     };
+
     NWWindow.prototype.capturePage = function (callback, options) {
       var cb = callback;
       if (!options)