Bug 930904 - Ensure the presShell resolution is recorded on the FrameMetrics for the root scrollable layer of the presShell. r=tn

Previously the code would only set the resolution on the FrameMetrics when
the scroll ID was equal to ROOT_SCROLL_ID. This only happens on the root
scrollable frame for a layer tree. However, with bug 732971 fixed, any presShell
can have a resolution associated with it, so we need to populate the mResolution
for any layer that is the root scrollable layer for a presShell.

On platforms like Fennec and Metro the content presShell is a sub-presShell
of the root presShell. The resolution is set on the content presShell, but would
not get populated on the FrameMetrics correctly because of this condition. The #ifdef
ANDROID hack a few lines below was used to work around this on Fennec but it
was broken on Metro. This change corrects the behaviour on both of these platforms.
Bug 930904 - Remove some old code for android that is now no-op'd. r=tn