[Mac] Poke KVO for prefs::kDownloadDefaultDirectory when resetting to default values.

chrome/browser/cocoa/preferences_window_controller.mm

Index: chrome/browser/cocoa/preferences_window_controller.mm
diff --git a/chrome/browser/cocoa/preferences_window_controller.mm b/chrome/browser/cocoa/preferences_window_controller.mm
index b7a56c01e8e600324ed3870137bf1905c7e211f7..c4f95bc35179b61aee2a8d0215b80a940f959e01 100644
--- a/chrome/browser/cocoa/preferences_window_controller.mm
+++ b/chrome/browser/cocoa/preferences_window_controller.mm
@@ -1378,6 +1378,11 @@ const int kDisabledIndex = 1;
   else if (*prefName == prefs::kMetricsReportingEnabled) {
     [self setMetricsRecording:metricsRecording_.GetValue() ? YES : NO];
   }
+  else if (*prefName == prefs::kDownloadDefaultDirectory) {
+    // Poke KVO.
+    [self willChangeValueForKey:@"defaultDownloadLocation"];
+    [self didChangeValueForKey:@"defaultDownloadLocation"];
+  }
   else if (*prefName == prefs::kPromptForDownload) {
     [self setAskForSaveLocation:askForSaveLocation_.GetValue() ? YES : NO];
   }