Sidebar item add bubble is anchored at wrong place

[simonhong]

When browser window doesn't have enough space to show item add bubble anchor position is changed implicitely.
Due to this bubble is shown like below.

Bubble should be anchored to add button like below.

STR:

1. Launch browser and reduce browser window
2. Hover mouce over add item button

[stephendonner]

Verified PASSED using

Brave	1.37.68 Chromium: 99.0.4844.35 (Official Build) nightly (64-bit)
Revision	f60a827ddb87f1c403e07713751a5551d5856ac0-refs/branch-heads/4844@{#579}
OS	Windows 11 Version 21H2 (Build 22000.527)

Followed the steps above and resized the window at various dimensions; confirmed the Add to Sidebar flyout was aligned with the + at each time.

example	example	example

---

Verified PASSED using

Brave	1.37.84 Chromium: 99.0.4844.51 (Official Build) beta (x86_64)
Revision	d537ec02474b5afe23684e7963d538896c63ac77-refs/branch-heads/4844@{#875}
OS	macOS Version 11.6.3 (Build 20G415)

Followed the steps above and resized the window at various dimensions; confirmed the Add to Sidebar flyout was aligned with the + at each time.

example	example	example

---

Verification passed on

Brave	1.37.95 Chromium: 99.0.4844.74 (Official Build) beta (64-bit)
Revision	fee9a47e86e981802390cb0d41c5ed7ea93c4f6f-refs/branch-heads/4844@{#1060}
OS	Ubuntu 18.04 LTS

Verified test plan from the description

confirmed the Add to Sidebar flyout was aligned with the +.