Fix runtime error in chrome://set-time dialog

If the dialog is opened from OS settings, it does not show the
timezone. However, the C++ code can sometimes send a timezone update
while the dialog is open.

Only update the timezone select if it is showing. Always send the
current timezone from C++ when the dialog opens, such that we can
adjust the time picker appropriately if the timezone changes.

Bug: 1015179
Test: added to JS tests
Change-Id: I1cd641c377a209c114d4c1359acbce775bf438c2
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2052565Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Commit-Queue: James Cook <jamescook@chromium.org>
Cr-Commit-Position: refs/heads/master@{#741097}

chrome/browser/resources/chromeos/set_time_dialog/set_time_dialog.js

@@ -137,7 +137,8 @@ Polymer({
     isTimezoneVisible_: {
       type: Boolean,
       readonly: true,
-      value: () => loadTimeData.getValue('currentTimezoneId') != '',
+      value: () =>
+          /** @type {boolean} */ (loadTimeData.getValue('showTimezone')),
     },
 
     /**
@@ -255,9 +256,11 @@ Polymer({
    * @private
    */
   setTimezone_(timezoneId) {
+    if (this.isTimezoneVisible_) {
       const timezoneSelect = this.$$('#timezoneSelect');
       assert(timezoneSelect.childElementCount > 0);
       timezoneSelect.value = timezoneId;
+    }
 
     const now = this.getInputTime_();
     const timezoneDelta = getTimezoneDelta(timezoneId, this.selectedTimezone_);

chrome/browser/ui/webui/chromeos/set_time_ui.cc

@@ -191,9 +191,8 @@ SetTimeUI::SetTimeUI(content::WebUI* web_ui) : WebDialogUI(web_ui) {
   values.Set("timezoneList", chromeos::system::GetTimezoneList());
 
   // If we are not logged in, we need to show the time zone dropdown.
-  // Otherwise, we can leave |currentTimezoneId| blank.
+  values.SetBoolean("showTimezone", SetTimeDialog::ShouldShowTimezone());
   std::string current_timezone_id;
-  if (SetTimeDialog::ShouldShowTimezone())
   CrosSettings::Get()->GetString(kSystemTimezone, &current_timezone_id);
   values.SetString("currentTimezoneId", current_timezone_id);
   values.SetDouble("buildTime", base::GetBuildTime().ToJsTime());

chrome/test/data/webui/set_time_dialog_test.js

@@ -52,6 +52,7 @@ suite('SetTimeDialog', function() {
   suiteSetup(function() {
     // Must use existing timezones in the test.
     loadTimeData.overrideValues({
+      showTimezone: true,
       currentTimezoneId: 'America/Sao_Paulo',
       timezoneList: [
         [
@@ -190,15 +191,12 @@ suite('SetTimeDialog', function() {
     expectEquals('America/Los_Angeles', newTimezone);
   });
 
-  suite('NullTimezone', () => {
+  suite('HideTimezone', () => {
     suiteSetup(() => {
-      loadTimeData.overrideValues({
-        currentTimezoneId: '',
-        timezoneList: [],
-      });
+      loadTimeData.overrideValues({showTimezone: false});
     });
 
-    test('SetDateNullTimezone', async () => {
+    test('SetDate', async () => {
       const dateInput = setTimeElement.$$('#dateInput');
       assertTrue(!!dateInput);
 
@@ -234,5 +232,12 @@ suite('SetTimeDialog', function() {
       // Verify the page didn't try to change the timezone.
       assertEquals(0, testBrowserProxy.getCallCount('setTimezone'));
     });
+
+    test('TimezoneUpdate', () => {
+      assertEquals(null, setTimeElement.$$('#timezoneSelect'));
+      cr.webUIListenerCallback(
+          'system-timezone-changed', 'America/Los_Angeles');
+      // No crash.
+    });
   });
 });