Fix RenderGeometryMap ASSERT in touch hit rect computation

RenderGeometryMap requires that the RenderView be pushed as the first mapping.
It helpfully does this for you when on the 'canMapBetweenRenderers' fast-path,
but not in the slow path.  Touch hit rect computation wasn't explicitly
pushing the RenderView and so could trigger this ASSERT (and potentially
other issues) if the first layer pushed doesn't satisfy the canMapBetweenRenderers
requirement (almost never the case in practice since the first layer is the
document element's layer).

BUG=339141

Review URL: https://codereview.chromium.org/129813009

git-svn-id: svn://svn.chromium.org/blink/trunk@166094 bbb929c8-8fbe-4397-9dbb-9b2b20218538