The parameter of the tester should have spaces in assert_selection()

When we run assert_selection(), the tester can take one parameter, but
it does not allow to have spaces. As a result, it cannot handle HTML
tags as parameter. This CL allows the parameter to have spaces.

BUG=none
TEST=editing/assert_selection.html

Review-Url: https://codereview.chromium.org/2155793002
Cr-Commit-Position: refs/heads/master@{#406226}
2 files changed