When the JS "Intl" API is available, use it to guess the timezone

Summary:
Ref T3025. Chrome gives us an easily-accessible, much better guess at which timezone the user is in.

Firefox also exposes "Intl" but this doesn't seem to be a reliable method to read the timezone.

Test Plan:
In Chrome, swapped my system date/time between zones, clicked the "reconcile" popup, got the dropdown prefilled accurately.

In Safari (no `Intl` API) got the normal flow with no default selected.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T3025

Differential Revision: https://secure.phabricator.com/D15962

resources/celerity/map.php

@@ -8,7 +8,7 @@
 return array(
   'names' => array(
     'core.pkg.css' => '8aeacc63',
-    'core.pkg.js' => '7b44c14f',
+    'core.pkg.js' => '50e9228e',
     'darkconsole.pkg.js' => 'e7393ebb',
     'differential.pkg.css' => '33da0633',
     'differential.pkg.js' => '4b7d8f19',
@@ -477,7 +477,7 @@ return array(
     'rsrc/js/core/behavior-choose-control.js' => '327a00d1',
     'rsrc/js/core/behavior-crop.js' => 'fa0f4fc2',
     'rsrc/js/core/behavior-dark-console.js' => 'f411b6ae',
-    'rsrc/js/core/behavior-detect-timezone.js' => 'ae9f2ec9',
+    'rsrc/js/core/behavior-detect-timezone.js' => '4c193c96',
     'rsrc/js/core/behavior-device.js' => 'bb1dd507',
     'rsrc/js/core/behavior-drag-and-drop-textarea.js' => '484a6e22',
     'rsrc/js/core/behavior-error-log.js' => '6882e80a',
@@ -602,7 +602,7 @@ return array(
     'javelin-behavior-dashboard-tab-panel' => 'd4eecc63',
     'javelin-behavior-day-view' => '5c46cff2',
     'javelin-behavior-desktop-notifications-control' => 'edd1ba66',
-    'javelin-behavior-detect-timezone' => 'ae9f2ec9',
+    'javelin-behavior-detect-timezone' => '4c193c96',
     'javelin-behavior-device' => 'bb1dd507',
     'javelin-behavior-differential-add-reviewers-and-ccs' => 'e10f8e18',
     'javelin-behavior-differential-comment-jump' => '4fdb476d',
@@ -1226,6 +1226,11 @@ return array(
       'javelin-util',
       'phabricator-shaped-request',
     ),
+    '4c193c96' => array(
+      'javelin-behavior',
+      'javelin-uri',
+      'phabricator-notification',
+    ),
     '4e3e79a6' => array(
       'javelin-behavior',
       'javelin-stratcom',
@@ -1744,11 +1749,6 @@ return array(
       'javelin-util',
       'phabricator-busy',
     ),
-    'ae9f2ec9' => array(
-      'javelin-behavior',
-      'javelin-uri',
-      'phabricator-notification',
-    ),
     'b003d4fb' => array(
       'javelin-behavior',
       'javelin-stratcom',

src/applications/settings/controller/PhabricatorSettingsTimezoneController.php

@@ -74,12 +74,20 @@ final class PhabricatorSettingsTimezoneController
         ->addCancelButton('/', pht('Done'));
     }
 
+    // If we have a guess at the timezone from the client, select it as the
+    // default.
+    $guess = $request->getStr('guess');
+    if (empty($options[$guess])) {
+      $guess = 'ignore';
+    }
+
     $form = id(new AphrontFormView())
       ->appendChild(
         id(new AphrontFormSelectControl())
           ->setName('timezone')
           ->setLabel(pht('Timezone'))
-          ->setOptions($options));
+          ->setOptions($options)
+          ->setValue($guess));
 
     return $this->newDialog()
       ->setTitle(pht('Adjust Timezone'))

webroot/rsrc/js/core/behavior-detect-timezone.js

@@ -45,6 +45,18 @@ JX.behavior('detect-timezone', function(config) {
 
     var uri = config.uri + offset + '/';
 
+    // Some browsers (notably, Chrome) expose an "Intl" API which gives us
+    // direct access to a timezone setting. If we are able to read this, use
+    // it to guess which timezone the user is in so we can prefill the
+    // dropdown.
+    try {
+      var guess = Intl.DateTimeFormat().resolvedOptions().timeZone;
+      uri = JX.$U(uri).setQueryParam('guess', guess);
+    } catch (error) {
+      // Ignore any errors here, we'll just make the user pick from the big
+      // list.
+    }
+
     new JX.Workflow(uri)
       .start();
   });