[code health] Remove "dangling" annotation from `delegate_` field.

This CL's main focus is removing the `AcrossTasksDanglingUntriaged`
annotation from the `WebContentsModalDialogManager::delegate_` field.
This is enabled by:

* Cleaning up delegates in `.../profile_picker_dice_sign_in_provider.cc`
  (based on https://crrev.com/c/5966395 and https://crrev.com/c/5142391,
  only changing the name of the method)
* Cleaning up delegates in `.../devtools_window.cc`
  (based on https://crrev.com/c/5966395 and https://crrev.com/c/5142391,
  but making the new code conditional on `!BUILDFLAG(IS_ANDROID)`
  because `Browser`, `BrowserList`, and `BrowserListObserver` only exist
  on desktop)
* Closing the DevTools window in `devtools_browsertest.cc`
  (based on https://crrev.com/c/5966395 and https://crrev.com/c/5142391,
  but going further, and also opportunistically removing some
  `DanglingUntriaged` annotations in that test suite).

Fixed: 41485289
Change-Id: Idaa280725a2fcb0377a22ac1413738c6dbf0263d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6501738
Reviewed-by: Andrey Kosyakov <caseq@chromium.org>
Reviewed-by: Colin Blundell <blundell@chromium.org>
Commit-Queue: Łukasz Anforowicz <lukasza@chromium.org>
Reviewed-by: David Roger <droger@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1456439}