fix(dropbox-auth): In Electron.

modules/API/external/electronPopupsConfig.json

             "url": "accounts.google.com"
         },
         "target": "electron"
+    },
+    "dropbox-auth": {
+        "matchPatterns": {
+            "url": "dropbox.com/oauth2/authorize"
+        },
+        "target": "electron"
     }
 }

react/features/dropbox/functions.web.js

     return new Promise(resolve => {
         const popup = window.open(authUrl, windowName);
 
-        gloabalNS.oauthCallbacks[windowName] = () => {
-            const returnURL = popup.location.href;
-
+        gloabalNS.oauthCallbacks[windowName] = url => {
             popup.close();
             delete gloabalNS.oauthCallbacks.windowName;
-            resolve(returnURL);
+            resolve(url);
         };
     });
 }

static/oauth.html

                 if (globalNS.oauthCallbacks
                     && typeof globalNS.oauthCallbacks[windowName]
                         === 'function') {
-                    globalNS.oauthCallbacks[windowName]();
+                    globalNS.oauthCallbacks[windowName](window.location.href);
                 }
             }
         })();