Readd 'UpdateFreWidgetSize' inside fre_controller.h.

This was removed because the FRE widget was being positioned incorrectly after initial load due to calling SetBounds. After removing, there was a regression in which the expanded content inside FRE got cut off because the widget size did not update although the web view size changed.

This change reverts it to how it performed previously; however, to address the positioning issue on Windows, we only call SetSize for the fre_widget_ rather than SetBounds.

Demo of the changes is located inside the bug!

Bug: 411199447, 409824244
Change-Id: I7ce01938edc2e40c86077958035f0fe26f0ea439
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6465757
Commit-Queue: Sana Akbani <sanaakbani@google.com>
Reviewed-by: Ian Wells <iwells@chromium.org>
Reviewed-by: Trevor Perrier <perrier@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1448587}