Add rounding to Plugin creation in SubframeLoader

Add rounding to Plugin creation in SubframeLoader
https://bugs.webkit.org/show_bug.cgi?id=82221

Reviewed by Eric Seidel.

Adding rounding to the LayoutSize used to construct Plugins in SubframeLoader. Plugins, which
are widgets, are always placed on integer boundaries, which means their sizes can be rounded
without considering their location. See https://trac.webkit.org/wiki/LayoutUnit for details.

No new tests. No change in behavior.

* loader/SubframeLoader.cpp:
(WebCore::SubframeLoader::loadMediaPlayerProxyPlugin):
(WebCore::SubframeLoader::createJavaAppletWidget):
(WebCore::SubframeLoader::loadPlugin):

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@112852 268f45cc-cd09-0410-ab3c-d52691b4dbfc