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This CL implements two P0 browser test cases
- It2MeBrowserTest.CancelShare
- It2MeBrowserTest.VerifyAccessCodeNotReusable

This only behavioral change in this CL is that we will always return INVALID_ACCESS_CODE
for It2Me Connections failed with HOST_IS_OFFLINE.
HOST_IS_OFFLINE suggests that the host portion of the access code
is invalid and we should hide this implementation detail from the user.

BUG=466849,466850

Review URL: https://codereview.chromium.org/1007543003

Cr-Commit-Position: refs/heads/master@{#320835}