Tests that modifying stylesheet text with multiple @import at-rules does not crash.

Initially added:
multiple-imports-edit-crash-1.css
multiple-imports-edit-crash-1.css
multiple-imports-edit-crash-2.css
Setting stylesheet text...
Removed:
multiple-imports-edit-crash-1.css
multiple-imports-edit-crash-1.css
multiple-imports-edit-crash-2.css
Added:
multiple-imports-edit-crash-1.css
multiple-imports-edit-crash-2.css