fix disable_gpu_frame_complete_metric flag (#9473)

- set the flag to true (metrics disabled) until downstream is ready
- make sure to exit the JobQueue thread before destroying it

BUGS=[464370498]

libs/utils/src/AsyncJobQueue.cpp

@@ -55,7 +55,10 @@ AsyncJobQueue::AsyncJobQueue(const char* name, Priority priority) {
 }
 
 AsyncJobQueue::~AsyncJobQueue() noexcept {
+    // wait for all pending callbacks to be called & terminate the thread
+    drainAndExit();
 #if !defined(__EMSCRIPTEN__)
+    assert_invariant(!mThread.joinable());
     assert_invariant(mQueue.empty());
 #endif
 }
@@ -94,6 +97,9 @@ bool AsyncJobQueue::isValid() const noexcept {
 void AsyncJobQueue::drainAndExit() {
 #if !defined(__EMSCRIPTEN__)
     std::unique_lock lock(mLock);
+    if (mExitRequested) {
+        return;
+    }
     // we request the service thread to exit, but we're guaranteed that it'll only exit
     // after all current callbacks are processed. In addition, once mExitRequested is set,
     // no new jobs can be added, so we can join the thread.