Add better handling of a TPM clear.

This adds a callback so that the user of TpmInit can receive a notification when the TPM initialization finishes.

Change-Id: I719810052e02536d54913950d0b9f053e6e3a01c

BUG=6883
TEST=(see change in cryptohome)

Review URL: http://codereview.chromium.org/3437016
4 files changed