Revert "Revert "ART: Start RuntimeCallbacks""

This reverts commit bf6331a45f730e1f1044af2ce43bceda660ae6fc.

Switch to using the mutator lock.

Bug: 31684920
Test: m test-art-host-gtest-runtime_callbacks_test
Test: art/tools/run-jdwp-tests.sh --mode=host --debug
Change-Id: I6ce0f71de2aa9f90cd23cfca7723a793b560b16b
diff --git a/runtime/debugger.h b/runtime/debugger.h
index 3b4a5e1..0135990 100644
--- a/runtime/debugger.h
+++ b/runtime/debugger.h
@@ -502,10 +502,6 @@
       REQUIRES_SHARED(Locks::mutator_lock_);
   static void PostException(mirror::Throwable* exception)
       REQUIRES_SHARED(Locks::mutator_lock_);
-  static void PostThreadStart(Thread* t)
-      REQUIRES_SHARED(Locks::mutator_lock_);
-  static void PostThreadDeath(Thread* t)
-      REQUIRES_SHARED(Locks::mutator_lock_);
   static void PostClassPrepare(mirror::Class* c)
       REQUIRES_SHARED(Locks::mutator_lock_);
 
@@ -707,6 +703,10 @@
     return instrumentation_events_;
   }
 
+  static ThreadLifecycleCallback* GetThreadLifecycleCallback() {
+    return &thread_lifecycle_callback_;
+  }
+
  private:
   static void ExecuteMethodWithoutPendingException(ScopedObjectAccess& soa, DebugInvokeReq* pReq)
       REQUIRES_SHARED(Locks::mutator_lock_);
@@ -725,6 +725,11 @@
       REQUIRES(!Locks::thread_list_lock_) REQUIRES_SHARED(Locks::mutator_lock_);
 
   static void DdmBroadcast(bool connect) REQUIRES_SHARED(Locks::mutator_lock_);
+
+  static void PostThreadStart(Thread* t)
+      REQUIRES_SHARED(Locks::mutator_lock_);
+  static void PostThreadDeath(Thread* t)
+      REQUIRES_SHARED(Locks::mutator_lock_);
   static void PostThreadStartOrStop(Thread*, uint32_t)
       REQUIRES_SHARED(Locks::mutator_lock_);
 
@@ -789,6 +794,14 @@
   static size_t exception_catch_event_ref_count_ GUARDED_BY(Locks::deoptimization_lock_);
   static uint32_t instrumentation_events_ GUARDED_BY(Locks::mutator_lock_);
 
+  class DbgThreadLifecycleCallback : public ThreadLifecycleCallback {
+   public:
+    void ThreadStart(Thread* self) OVERRIDE REQUIRES_SHARED(Locks::mutator_lock_);
+    void ThreadDeath(Thread* self) OVERRIDE REQUIRES_SHARED(Locks::mutator_lock_);
+  };
+
+  static DbgThreadLifecycleCallback thread_lifecycle_callback_;
+
   DISALLOW_COPY_AND_ASSIGN(Dbg);
 };