[Sync] Add support for only prompting for passphrase once
If the finch experiment is set, we'll only use the native android
notification once, after which we stop prompting for a passphrase.
The user can still resolve their passphrase error via the settings.
This patch also introduces histograms to track how people typically
interact with the passphrase dialog. In particular, how often do
they not even try to enter a passphrase, enter the wrong passphrase,
succeed, or follow the dashboard reset link.
BUG=481562
Review URL: https://codereview.chromium.org/
1114753002
Cr-Commit-Position: refs/heads/master@{#327935}