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/ui/webui/chromeos/crostini_upgrader
This CL was uploaded by git cl split.

R=joelhockey@chromium.org

Change-Id: Ia2ce23323e4f98ea6c9205d707d53866026e6244
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2434775
Auto-Submit: Kevin McNee <mcnee@chromium.org>
Reviewed-by: Nicholas Verne <nverne@chromium.org>
Commit-Queue: Nicholas Verne <nverne@chromium.org>
Cr-Commit-Position: refs/heads/master@{#811506}

chrome/browser/ui/webui/chromeos/crostini_upgrader/crostini_upgrader_dialog_browsertest.cc

@@ -43,7 +43,7 @@ class CrostiniUpgraderDialogBrowserTest : public CrostiniDialogBrowserTest {
 
   chromeos::CrostiniUpgraderDialog* GetCrostiniUpgraderDialog() {
     auto url = GURL{chrome::kChromeUICrostiniUpgraderUrl};
-    return reinterpret_cast<chromeos::CrostiniUpgraderDialog*>(
+    return static_cast<chromeos::CrostiniUpgraderDialog*>(
         chromeos::SystemWebDialogDelegate::FindInstance(url.spec()));
   }