GC triggering performance optimizations

Copy the correct starting heap size at process init.
Interfaces to set GC/managed heap parameters.

Change-Id: Idc02ef35c6045c129addcac17628eefffe958805
(cherry picked from commit 71c3f30fc9ad6ecaf534a02b6e795d86628d923b)
(cherry picked from commit a93fe7200b5df163e13e11059555ddcbdcbbf808)
(cherry picked from commit cc68d4a09b89aa71e5dd08ee6a220200f4e084e9)

Conflicts:
	core/java/android/app/ActivityThread.java