cppgc-js: Explicitly initialize a moved-away struct

The struct is reused across various GC cycles and std::move() may leave
the vector in valid but unspecified state.

Change-Id: I3c40795be7397d015b96116d3549953024b98808
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3160197
Auto-Submit: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Anton Bikineev <bikineev@chromium.org>
Reviewed-by: Omer Katz <omerkatz@chromium.org>
Reviewed-by: Anton Bikineev <bikineev@chromium.org>
Cr-Commit-Position: refs/heads/main@{#76811}

src/heap/cppgc-js/cpp-heap.cc

@@ -254,6 +254,7 @@ void CppHeap::MetricRecorderAdapter::AddMainThreadEvent(
   if (incremental_mark_batched_events_.events.size() == kMaxBatchedEvents) {
     recorder->AddMainThreadEvent(std::move(incremental_mark_batched_events_),
                                  GetContextId());
+    incremental_mark_batched_events_ = {};
   }
 }
 
@@ -272,6 +273,7 @@ void CppHeap::MetricRecorderAdapter::AddMainThreadEvent(
   if (incremental_sweep_batched_events_.events.size() == kMaxBatchedEvents) {
     recorder->AddMainThreadEvent(std::move(incremental_sweep_batched_events_),
                                  GetContextId());
+    incremental_sweep_batched_events_ = {};
   }
 }
 
@@ -282,10 +284,12 @@ void CppHeap::MetricRecorderAdapter::FlushBatchedIncrementalEvents() {
   if (!incremental_mark_batched_events_.events.empty()) {
     recorder->AddMainThreadEvent(std::move(incremental_mark_batched_events_),
                                  GetContextId());
+    incremental_mark_batched_events_ = {};
   }
   if (!incremental_sweep_batched_events_.events.empty()) {
     recorder->AddMainThreadEvent(std::move(incremental_sweep_batched_events_),
                                  GetContextId());
+    incremental_sweep_batched_events_ = {};
   }
 }