Add zygote space as its own space type.

Helps prevent errors caused from doing invalid operations on the
old alloc space.

Removed some duplicated code in mark_sweep.cc and semi_space.cc.

Change-Id: I67a772cab30d698744c918aad581053f282a4a99
diff --git a/runtime/gc/accounting/space_bitmap.cc b/runtime/gc/accounting/space_bitmap.cc
index 99800fc..b831843 100644
--- a/runtime/gc/accounting/space_bitmap.cc
+++ b/runtime/gc/accounting/space_bitmap.cc
@@ -128,9 +128,9 @@
 //
 // The callback is not permitted to increase the max of either bitmap.
 void SpaceBitmap::SweepWalk(const SpaceBitmap& live_bitmap,
-                           const SpaceBitmap& mark_bitmap,
-                           uintptr_t sweep_begin, uintptr_t sweep_end,
-                           SpaceBitmap::SweepCallback* callback, void* arg) {
+                            const SpaceBitmap& mark_bitmap,
+                            uintptr_t sweep_begin, uintptr_t sweep_end,
+                            SpaceBitmap::SweepCallback* callback, void* arg) {
   CHECK(live_bitmap.bitmap_begin_ != NULL);
   CHECK(mark_bitmap.bitmap_begin_ != NULL);
   CHECK_EQ(live_bitmap.heap_begin_, mark_bitmap.heap_begin_);