BackingStoreSkia: Use skia for painting in RenderWidgetHostViewViews.

Instead of directly painting to X, paint to the skia canvas from RWHVV. This
will make it easier to apply transformation to views in a uniform way, without
requiring any special-casing for RWHVV.

BUG=none
TEST=none

Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=74840

Review URL: http://codereview.chromium.org/6246129

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@74859 0039d316-1c4b-4281-b951-d872f2087c98