Changed views::BubbleFrameView::CreateCloseButton() to return std::unique_ptr

In order to better convey property object ownership,
changed CreateCloseButton() to return std::unique_ptr.

Bug: 948266
Change-Id: I781ee11dd46d80d41d61eb65e88ce265d88313e1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1575878
Reviewed-by: Dana Fried <dfried@chromium.org>
Commit-Queue: Yeol Park <peary2@gmail.com>
Cr-Commit-Position: refs/heads/master@{#653057}
3 files changed