cppgc-js: Set stack start

Set stack start as otherwise TracedReference from stack would not be
kept alive.

Bug: chromium:1220744, chromium:1056170
Change-Id: I99d54ac44b3f7cb4aa9732eb9260b918193a68e2
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2972728Reviewed-by: Dominik Inführ <dinfuehr@chromium.org>
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#75249}

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

@@ -14,6 +14,7 @@
 #include "include/v8.h"
 #include "src/base/logging.h"
 #include "src/base/macros.h"
+#include "src/base/platform/platform.h"
 #include "src/base/platform/time.h"
 #include "src/execution/isolate-inl.h"
 #include "src/flags/flags.h"
@@ -323,6 +324,7 @@ void CppHeap::AttachIsolate(Isolate* isolate) {
   isolate_->heap()->local_embedder_heap_tracer()->SetWrapperDescriptor(
       wrapper_descriptor_);
   SetMetricRecorder(std::make_unique<MetricRecorderAdapter>(*this));
+  SetStackStart(base::Stack::GetStackStart());
   no_gc_scope_--;
 }
 

test/unittests/heap/unified-heap-unittest.cc

@@ -132,6 +132,22 @@ TEST_F(UnifiedHeapTest, WriteBarrierCppToV8Reference) {
             wrappable->wrapper()->GetAlignedPointerFromInternalField(1));
 }
 
+TEST_F(UnifiedHeapTest, TracedReferenceRetainsFromStack) {
+  v8::HandleScope scope(v8_isolate());
+  v8::Local<v8::Context> context = v8::Context::New(v8_isolate());
+  v8::Context::Scope context_scope(context);
+  TracedReference<v8::Object> holder;
+  {
+    v8::HandleScope scope(v8_isolate());
+    auto local = v8::Object::New(v8_isolate());
+    EXPECT_TRUE(local->IsObject());
+    holder.Reset(v8_isolate(), local);
+  }
+  CollectGarbageWithEmbedderStack(cppgc::Heap::SweepingType::kAtomic);
+  auto local = holder.Get(v8_isolate());
+  EXPECT_TRUE(local->IsObject());
+}
+
 TEST_F(UnifiedHeapDetachedTest, AllocationBeforeConfigureHeap) {
   auto heap = v8::CppHeap::Create(
       V8::GetCurrentPlatform(),