Modify autofill update credential pixel to include backfilled parameter

[CDRussell]

Task/Issue URL: https://app.asana.com/0/1202926619870900/1208976665268815/f

Description

Steps to test this PR

Logcat filter: message~:"Pixel sent: m.autofill.logins.update.password.inline" | message~:"partial save" | message~:"backfill"

Updating password (with backfilling)

• Add a single login for autofill.me with username=test and set a password for it (deleting any others you have)
• Visit https://autofill.me/form/login-simple and decline offer to autofill
• Enter username test
• Leave password empty, and hit the Login button (to simulate a partial save)
• Clear the username
• Enter a different password than what is stored already
• Hit the Login button
• Verify in log that for m_autofill_logins_update_password_inline_displayed, backfilled=true
• Dismiss the dialog, and verify that for m_autofill_logins_update_password_inline_dismissed, backfilled=true
• Repeat from Clear the username step, and this time accept to update the password. Verify that m_autofill_logins_update_password_inline_confirmed has backfilled=true

Updating password (without backfilling)

• Add a single login for autofill.me with username=test and set a password for it (deleting any others you have)
• Visit https://autofill.me/form/login-simple and decline offer to autofill
• Enter username test
• Enter a different password than what is stored already
• Hit the Login button
• Verify in log that for m_autofill_logins_update_password_inline_displayed, backfilled=false
• Dismiss the dialog, and verify that for m_autofill_logins_update_password_inline_dismissed, backfilled=false
• Repeat and this time accept to update the password. Verify that m_autofill_logins_update_password_inline_confirmed has backfilled=false

[CDRussell]

Warning

This pull request is not mergeable via GitHub because a downstack PR is open. Once all requirements are satisfied, merge this PR as a stack on Graphite.
Learn more

• Modify autofill update credential pixel to include backfilled parameter #5392 👈 (View in Graphite)
• Autofill: Increase ratio of complete credential saves #5386
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