Add support for jemalloc.

This is good enough to get dalvik to compile, but it still requires
more work to make it really work.

Bug: 981363
Change-Id: I411428a2e859c1f474fa0d7aaf406979bba9ed72
Merge "Add support for jemalloc."
Support new VMRuntime native method

Implements isCheckJniEnabled method.

Bug: 14888999
Bug: 14888124
Change-Id: I8a2d3f22f84a093be2fbc74464af6aa7b2a2bebb
Merge "Support new VMRuntime native method"
auto-merger: merge in from aosp/master