Trim arenas for JIT

Moved arena pool into the runtime. Added arena trimming to arena
pool. When called, this madvises the used memory.

Changed the JIT compiler to trim arenas after compilation. Changed
the arena mmap name to dalvik-LinearAlloc.

Native PSS before:
  80353 kB: Native
  80775 kB: Native
  78116 kB: Native
After:
  73357 kB: Native
  70181 kB: Native
  70306 kB: Native

Bug: 17950037
Bug: 17643507
Bug: 19264997

Change-Id: I63e7a898fd6e909c2c677fa57b5917a7b1398930
diff --git a/runtime/runtime.cc b/runtime/runtime.cc
index 70de0db..ac1040d 100644
--- a/runtime/runtime.cc
+++ b/runtime/runtime.cc
@@ -251,6 +251,7 @@
     VLOG(jit) << "Deleting jit";
     jit_.reset(nullptr);
   }
+  arena_pool_.reset();
 
   // Shutdown the fault manager if it was initialized.
   fault_manager.Shutdown();
@@ -787,6 +788,7 @@
   max_spins_before_thin_lock_inflation_ =
       runtime_options.GetOrDefault(Opt::MaxSpinsBeforeThinLockInflation);
 
+  arena_pool_.reset(new ArenaPool);
   monitor_list_ = new MonitorList;
   monitor_pool_ = MonitorPool::Create();
   thread_list_ = new ThreadList;