• Sketch in a page layout and grid to house the tab-pickup region
• Add a tabs-pickup module with custom elements for the deck of cards that is the setup flow
• and a container/controller with placeholder tab-pickup logic, driven by a 'myfirefox.syncsetup' pref

Backed out for causing bc failures on browser_all_files_referenced.js and browser_parsable_script.js

Push with failures: https://treeherder.mozilla.org/jobs?repo=autoland&resultStatus=testfailed%2Cbusted%2Cexception%2Cusercancel&revision=aa07bcb8d62d8e28fb52741428c1affce42f327b&selectedTaskRun=PvhC2kitS8S9Vxwr5R_Kpw.0

Failure log: https://treeherder.mozilla.org/logviewer?job_id=374108288&repo=autoland

Backout link: https://hg.mozilla.org/integration/autoland/rev/2181725c0a4f0a67c9d3c706de9fb512e2694c5f

[task 2022-04-11T18:27:28.475Z] 18:27:28     INFO - TEST-UNEXPECTED-FAIL | browser/base/content/test/static/browser_all_files_referenced.js | unreferenced file: chrome://browser/content/tabs-pickup.js - 
[task 2022-04-11T18:27:28.476Z] 18:27:28     INFO - Stack trace:
[task 2022-04-11T18:27:28.477Z] 18:27:28     INFO - chrome://mochikit/content/browser-test.js:test_ok:1394
[task 2022-04-11T18:27:28.478Z] 18:27:28     INFO - chrome://mochitests/content/browser/browser/base/content/test/static/browser_all_files_referenced.js:checkAllTheFiles:1044
[task 2022-04-11T18:27:28.483Z] 18:27:28     INFO - ignored unused whitelist entry: resource://app/blocklist.xml
[task 2022-04-11T18:27:28.485Z] 18:27:28     INFO - ignored unused whitelist entry: resource://gre/gmp-clearkey/0.1/manifest.json
[task 2022-04-11T18:27:28.487Z] 18:27:28     INFO - ignored unused whitelist entry: resource://gre/res/test.properties
[task 2022-04-11T18:27:28.488Z] 18:27:28     INFO - missing file: chrome://aboutsync/content/AboutSyncRedirector.js

[task 2022-04-11T18:27:41.696Z] 18:27:41     INFO - TEST-UNEXPECTED-FAIL | browser/base/content/test/static/browser_parsable_script.js | Script error reading jar:file:///builds/worker/workspace/build/application/firefox/browser/omni.ja!/chrome/browser/content/browser/myfirefox.js: SyntaxError: import declarations may only appear at top level of a module - 
[task 2022-04-11T18:27:41.696Z] 18:27:41     INFO - Stack trace:
[task 2022-04-11T18:27:41.696Z] 18:27:41     INFO - chrome://mochikit/content/browser-test.js:test_ok:1394
[task 2022-04-11T18:27:41.697Z] 18:27:41     INFO - chrome://mochitests/content/browser/browser/base/content/test/static/browser_parsable_script.js:parsePromise/promise</xhr.onreadystatechange:87
[task 2022-04-11T18:27:41.701Z] 18:27:41     INFO - Checking script jar:file:///builds/worker/workspace/build/application/firefox/browser/omni.ja!/chrome/devtools/modules/devtools/shared/webconsole/parser-helper.js
[task 2022-04-11T18:27:41.702Z] 18:27:41     INFO - Checking script jar:file:///builds/worker/workspace/build/application/firefox/browser/omni.ja!/chrome/devtools/modules/devtools/shared/commands/script/script-command.js
[task 2022-04-11T18:27:41.703Z] 18:27:41     INFO - Checking script jar:file:///builds/worker/workspace/build/application/firefox/browser/omni.ja!/chrome/devtools/modules/devtools/client/shared/widgets/Chart.js

https://hg.mozilla.org/mozilla-central/rev/7794dcdf5ca7

Clearing need-info. Thanks for the backout.