Fixed ArtMethod::GetQuickFrameInfo() for proxy methods

If we call ArtMethod::GetQuickFrameInfo() on a proxy constructor when
instrumentation stubs are installed, the entry point returned by
Instrumentation::GetQuickCodeFor() would be a artQuickProxyInvokeHandler,
and not a regular quick oat code pointer. This patch adds special handling
for proxy constructors to always compute frame info from the regular quick
code entry point. (These entry points are never updated by instrumentation
for proxy methods.)

Change-Id: I8e51f5622b6d327037d5c968b07505b2bf4ac737
Signed-off-by: Daniel Mihalyi <daniel.mihalyi@mattakis.com>