Component installer: Verify installation when searching for latest dir.

If a version folder is corrupted (e.g. the component binary is deleted
accidently), we should not call the component installer with ComponentReady()
with this folder. Instead, we should remove the corrupted folder and trigger a
new update.

Review URL: https://codereview.chromium.org/138383004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@245766 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 245766