This CL initialises the change theme button in
correct place and adds the functionality to change
theme after the data load.

Bug: v8:10644

Change-Id: I7397933ff9d12a2ac270d025df1b3327801d89be
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2336800Reviewed-by: Camillo Bruni <cbruni@chromium.org>
Commit-Queue: Zeynep Cankara <zcankara@google.com>
Cr-Commit-Position: refs/heads/master@{#69238}