[Save to Drive] Route upload progress to toolbar icon button

This CL connects the Drive upload progress data to the
`ViewerSaveToDriveControlsElement`, enabling the circular progress
indicator to display the real-time upload status to the user.

This change also includes a small refactoring of how the
`ViewerSaveToDriveControlsElement` accepts the progress value, improving
code clarity.

Change-Id: I00de148fcbe4c45055e8ce0ec5963e6a6a9752c6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6837898
Reviewed-by: Andy Phan <andyphan@chromium.org>
Reviewed-by: Lei Zhang <thestig@chromium.org>
Commit-Queue: Yihong Guo <yhguo@google.com>
Cr-Commit-Position: refs/heads/main@{#1505275}