Fail in the right place when we cannot allocate a mark stack.

Previously we'd keep going and then crash when dereferencing
the mark stack later. I expected dalvikvm to throw an OutOfMemoryError
in this scenario but it also aborts.

Change-Id: I3cd995113561f40b191fcb51ecfcb1f032bed4ec
diff --git a/src/mark_sweep.cc b/src/mark_sweep.cc
index bf4f1bf..d44796c 100644
--- a/src/mark_sweep.cc
+++ b/src/mark_sweep.cc
@@ -22,12 +22,8 @@
 
 namespace art {
 
-bool MarkSweep::Init() {
+void MarkSweep::Init() {
   mark_stack_ = MarkStack::Create();
-  if (mark_stack_ == NULL) {
-    return false;
-  }
-
   mark_bitmap_ = Heap::GetMarkBits();
   live_bitmap_ = Heap::GetLiveBits();
 
@@ -36,8 +32,6 @@
   // TODO: if concurrent, enable card marking in compiler
 
   // TODO: check that the mark bitmap is entirely clear.
-
-  return true;
 }
 
 inline void MarkSweep::MarkObject0(const Object* obj, bool check_finger) {