Add .gitignore for generated files.
Add .gitignore for generated files.

BUG=None

Change-Id: I29938d3976302ebe9e20f995e1613b0fd69fbc3e

vapier/chrome-ext-wicked-good-unarchiver,vapier/chrome-ext-wicked-good-unarchiver,vapier/chrome-ext-wicked-good-unarchiver,vapier/chrome-ext-wicked-good-unarchiver,vapier/chrome-ext-wicked-good-unarchiver