Set the initial dialog width when the sign-in email confirmation dialog is presented.

chrome/browser/ui/webui/signin/signin_email_confirmation_dialog.cc

Index: chrome/browser/ui/webui/signin/signin_email_confirmation_dialog.cc
diff --git a/chrome/browser/ui/webui/signin/signin_email_confirmation_dialog.cc b/chrome/browser/ui/webui/signin/signin_email_confirmation_dialog.cc
index 62074313d3149d785c6b28847a73ebbd3fa40361..57dc18913769987d8c4aae97b552abe82fa0077a 100644
--- a/chrome/browser/ui/webui/signin/signin_email_confirmation_dialog.cc
+++ b/chrome/browser/ui/webui/signin/signin_email_confirmation_dialog.cc
@@ -140,8 +140,13 @@ void SigninEmailConfirmationDialog::GetWebUIMessageHandlers(
     std::vector<content::WebUIMessageHandler*>* handlers) const {}
 
 void SigninEmailConfirmationDialog::GetDialogSize(gfx::Size* size) const {
-  // Avoid setting a dialog size in here as this dialog auto-resizes (see
-  // method |SigninEmailConfirmationDialog::Show|.
+  DCHECK(size);
+
+  // Set the dialog width if it's not set, so that the dialog is center-aligned
+  // horizontally when it appears. Avoid setting a dialog height in here as
+  // this dialog auto-resizes.
+  if (size->IsEmpty())
+    size->set_width(kDialogWidth);
 }
 
 std::string SigninEmailConfirmationDialog::GetDialogArgs() const {