Avoid a use before initialization in mark sweep.

MarkSweep::GetName reads is_concurrent_, we pass GetName to the timing loggers
but before is_concurrent_ is initialized. Reorder is_concurrent_ to fix.

Change-Id: I98a65534a86ad18789aa0624808235f6b68c58d6
diff --git a/src/gc/mark_sweep.cc b/src/gc/mark_sweep.cc
index 35e75cb..25b4b78 100644
--- a/src/gc/mark_sweep.cc
+++ b/src/gc/mark_sweep.cc
@@ -137,9 +137,9 @@
       gc_barrier_(new Barrier(0)),
       large_object_lock_("mark sweep large object lock", kMarkSweepLargeObjectLock),
       mark_stack_expand_lock_("mark sweep mark stack expand lock"),
+      is_concurrent_(is_concurrent),
       timings_(GetName(), true),
-      cumulative_timings_(GetName()),
-      is_concurrent_(is_concurrent) {
+      cumulative_timings_(GetName()) {
   cumulative_timings_.SetName(GetName());
   ResetCumulativeStatistics();
 }