Use static_cast instead of reinterpret_cast for downcasting

static_cast is better suited for downcasting since it can check that the
types are related.

/chrome/browser/chromeos/crostini
This CL was uploaded by git cl split.

R=hollingum@google.com

Change-Id: I5fa53d165710036fd346b5d864251502ce57cbc0
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2435979
Auto-Submit: Kevin McNee <mcnee@chromium.org>
Reviewed-by: Nic Hollingum <hollingum@google.com>
Commit-Queue: Nic Hollingum <hollingum@google.com>
Cr-Commit-Position: refs/heads/master@{#811414}

chrome/browser/chromeos/crostini/crostini_upgrade_available_notification_unittest.cc

@@ -60,7 +60,7 @@ class CrostiniUpgradeAvailableNotificationTest
 
   chromeos::CrostiniUpgraderDialog* GetCrostiniUpgraderDialog() {
     auto url = GURL{chrome::kChromeUICrostiniUpgraderUrl};
-    return reinterpret_cast<chromeos::CrostiniUpgraderDialog*>(
+    return static_cast<chromeos::CrostiniUpgraderDialog*>(
         chromeos::SystemWebDialogDelegate::FindInstance(url.spec()));
   }