[Sync] Automatically clear passphrase required reason for first time sync
[Sync] Automatically clear passphrase required reason for first time sync

In SetEncryptionPassphrase, if the passphrase required reason is
REASON_ENCRYPTION (and we're not attempting to do an invalid passphrase
transition) we know the passphrase will be accepted. As a result we can
automatically clear the passphrase required reason before the
OnPassphraseAccepted call gets sent.

BUG=121190
TEST=manual first time sync


Review URL: http://codereview.chromium.org/9968020

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@130198 0039d316-1c4b-4281-b951-d872f2087c98

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