Make Crankshaft configurable at compile-time.

Add a flag in Android.mk to enable crankshaft in V8.

Note that Crankshaft and snapshotting cannot currently be used
at the same time. For now, leave Crankshaft disabled by default.

Change-Id: I84fcc02882e1b16cd0bc783d778ffbcc4531c868
4 files changed