The class ViewportFrame doesn't have ns-prefix, so it's better to drop the
ns-prefix in the file names to avoid confusion.
MozReview-Commit-ID: 8Jrmfzb3tVR
--HG--
rename : layout/generic/nsViewportFrame.cpp => layout/generic/ViewportFrame.cpp
rename : layout/generic/nsViewportFrame.h => layout/generic/ViewportFrame.h
extra : rebase_source : d2c6a80275d696a2886983a4bbb46821784c7fe6