Log when non-current version of main.json is replaced

[davidsbailey]

Background

The problem scenario

1. open project in tab A, write "// version 1", and press run

2. still in tab A, write "// version 2", and press run

3. open the same project in tab B, write "// version 3 with many changes", and press run

4. in tab A, write "// version 4" and press run

   EXPECTED: warning that project is being edited in multiple places
   ACTUAL: no warning

5. go back to tab B and refresh the page

   EXPECTED: "version 3 ..." remains visible, or a warning is displayed with link to version history
   ACTUAL: "version 3 ..." disappears, though still exists in version history

How project versions work

• when loading a project, read the latest version (if one exists) and then create an identical "current" version (see currentSourceVersionId)
• when saving changes to a project, write a newer version, and remove the "current" version
• do nothing special when reloading/leaving the page. by "forgetting" the current version id, it can no longer be replaced when the project is run, effectively making it a persistent entry in the version history.

Description

Start logging to Firehose when the problem sequence happens. Do this by detecting when the version of main.json being replaced is not the latest version of that file.

For each tab, remember the server timestamp from the first time it saved a copy of the current project (firstSaveTimestamp). Persist this timestamp only when logging to Firehose, in order to

1. uniquely identify multiple tabs;
2. enable inferring which entries in version history were created by which tab; and
3. avoid persisting this timestamp when no problem is detected.

This PR gathers logging information only, and does not fix the EXPECTED/ACTUAL discrepancies listed above.

[islemaster]

👍 Looks good, looking forward to having this data.

[davidsbailey]

@islemaster , I've added the tab id when replacing non-current versions, and it appears to be (1) unique between tabs and (2) consistent across reloads within the same tab. PTAL?

[islemaster]

Cool. Tab ID implementation looks good.

[davidsbailey]

if reverting, will also need to revert e748f05 .