Move the ResourceUsageOverlay out of the way by default.

Move the ResourceUsageOverlay out of the way by default.
<https://webkit.org/b/150776>

Reviewed by Darin Adler.

Have the ResourceUsageOverlay show up in the bottom center of the viewport
by default, instead of the top left. This way, you won't have to drag it
out of the way all the time.

* page/ResourceUsageOverlay.cpp:
(WebCore::ResourceUsageOverlay::ResourceUsageOverlay):
(WebCore::ResourceUsageOverlay::initialize):
* page/ResourceUsageOverlay.h:
* page/cocoa/ResourceUsageOverlayCocoa.mm:
(WebCore::ResourceUsageOverlay::platformInitialize):

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@191861 268f45cc-cd09-0410-ab3c-d52691b4dbfc