Fix flakiness of SelectFileDialogExtensionBrowserTest.SelectFileAndCancel.
Previously the test waits for destruction of render view host to check if the
dialog has been closed or not. But test log shows there is a race and we cannot
ensure the extension dialog has been closed even if its render view host is
closed.
The CL let the test wait for SelectionFileDialog::Listener's call instead, where
we can ensure the dialog has been closed.
BUG=453613
TEST=SelectFileDialogExtensionBrowserTest.SelectFileAndCancel
Review URL: https://codereview.chromium.org/
902493002
Cr-Commit-Position: refs/heads/master@{#314510}