Reduce code size by sharing slow paths.

Reduce code size by sharing slow paths.

Rationale:
Sharing identical slow path code reduces code size.

Background:
Currently, slow paths with the same dex-pc, same physical register
spilling code, and identical stack maps are shared (making this
only useful for deopt slow paths). The newly introduced mechanism
is sufficiently general to allow future improvements by e.g.
allowing different dex-pc (by passing this to runtime) or even
the kind of slow paths (by passing runtime addresses to the slowpath).

Change-Id: I819615c47b4fd98440a241f681f93e4fc22d12e0