ART: Add GC callbacks

Add start and end of pause callbacks.

Fix setup and missing functions in test 907.

Bug: 31684633
Test: m test-art-host
Test: m test-art-host-run-test-908-gc-start-finish
Change-Id: I1d8872ef9cd6914de7fb033cd873f8d5cb48ea17
diff --git a/runtime/openjdkjvmti/events.h b/runtime/openjdkjvmti/events.h
index 3212b12..07d6bfd 100644
--- a/runtime/openjdkjvmti/events.h
+++ b/runtime/openjdkjvmti/events.h
@@ -28,6 +28,7 @@
 
 struct ArtJvmTiEnv;
 class JvmtiAllocationListener;
+class JvmtiGcPauseListener;
 
 struct EventMask {
   static constexpr size_t kEventsSize = JVMTI_MAX_EVENT_TYPE_VAL - JVMTI_MIN_EVENT_TYPE_VAL + 1;
@@ -103,6 +104,7 @@
   EventMask global_mask;
 
   std::unique_ptr<JvmtiAllocationListener> alloc_listener_;
+  std::unique_ptr<JvmtiGcPauseListener> gc_pause_listener_;
 };
 
 }  // namespace openjdkjvmti