Desktop Page Info/Harmony: Show close button for internal pages.

The Harmony version of Page Info for internal Chrome pages (chrome://,
chrome-extension:// and view-source:// pages) show a close button. Update the
code to match this.

This patch also adds TestBrowserDialog tests for the latter two cases described
above (internal extension and view source pages).

See screenshot -
https://drive.google.com/file/d/18RZnMiHCu-rCX9N6DLUpu4mkFWguh1xm/view?usp=sharing

Bug: 535074
Change-Id: I55e5f1aa682fd4ec85f7b65ac88f5a4f5906fe53
Reviewed-on: https://chromium-review.googlesource.com/759624
Commit-Queue: Patti <patricialor@chromium.org>
Reviewed-by: Trent Apted <tapted@chromium.org>
Cr-Commit-Position: refs/heads/master@{#516624}
PageInfoBubbleView::~PageInfoBubbleView() {}

PageInfoBubbleView::~PageInfoBubbleView() {}
