Fix GC performance regression

Enable CMS and fix performance regression due to recursive marking image spaces. Dependent on my java change list.

Change-Id: I4765792aa8226e811ac158f04ab88217db755573
diff --git a/src/runtime.cc b/src/runtime.cc
index 784a3f6..1a66951 100644
--- a/src/runtime.cc
+++ b/src/runtime.cc
@@ -69,6 +69,7 @@
       system_class_loader_(NULL),
       shutting_down_(false),
       started_(false),
+      finished_starting_(false),
       vfprintf_(NULL),
       exit_(NULL),
       abort_(NULL),
@@ -573,6 +574,8 @@
   Thread::Current()->GetJniEnv()->locals.AssertEmpty();
 
   VLOG(startup) << "Runtime::Start exiting";
+
+  finished_starting_ = true;
 }
 
 void Runtime::DidForkFromZygote() {