Fix gap in outline around side panel content and corner radius.

Draw the outline using drawRRect on the PaintCanvas to match how the
clipped region is being done and take the device scale factor into
account when setting the corner radius for the clipped region and
outline.

Bug: 1457249
Change-Id: I39e287b9be190a5cf65f9a4076e9049474684305
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4776876


Commit-Queue: Caroline Rising <corising@chromium.org>
Code-Coverage: findit-for-me@appspot.gserviceaccount.com <findit-for-me@appspot.gserviceaccount.com>
Reviewed-by: David Pennington <dpenning@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1184816}