Fix a heap lock/thread list lock deadlock.

We had an uncaught OOME whose uncaught exception handler -- running
with the thread lock held -- was trying to cause a GC while some
other thread had the heap lock and was waiting for the thread list
lock.

Change-Id: I22177129562268837127d9edcc63ef5e93054bdf
diff --git a/src/heap.cc b/src/heap.cc
index 73b6640..d9db50b 100644
--- a/src/heap.cc
+++ b/src/heap.cc
@@ -584,6 +584,10 @@
   SetIdealFootprint(target_size);
 }
 
+uint32_t Heap::GetLockOwner() {
+  return lock_->GetOwner();
+}
+
 void Heap::Lock() {
   // Grab the lock, but put ourselves into Thread::kVmWait if it looks
   // like we're going to have to wait on the mutex. This prevents