[heap-profiler] Annotate "const/let" refs in top level script context.

This patch extends ExtractContextReferences to handle all declaration
contexts, not only function/module/eval contexts.

Bug: chromium:817954
Change-Id: Ibe2827a9d6b2939552da26a60df959c9b22ea059
Reviewed-on: https://chromium-review.googlesource.com/962763
Commit-Queue: Ulan Degenbaev <ulan@chromium.org>
Reviewed-by: Alexei Filippov <alph@chromium.org>
Cr-Commit-Position: refs/heads/master@{#51945}

src/profiler/heap-snapshot-generator.cc

@@ -1033,8 +1033,8 @@ void V8HeapExplorer::ExtractJSWeakCollectionReferences(int entry,
 }
 
 void V8HeapExplorer::ExtractContextReferences(int entry, Context* context) {
-  if (context == context->declaration_context()) {
-    ScopeInfo* scope_info = context->closure()->shared()->scope_info();
+  if (!context->IsNativeContext() && context->is_declaration_context()) {
+    ScopeInfo* scope_info = context->scope_info();
     // Add context allocated locals.
     int context_locals = scope_info->ContextLocalCount();
     for (int i = 0; i < context_locals; ++i) {

test/cctest/test-heap-profiler.cc

@@ -2891,6 +2891,37 @@ TEST(JSPromise) {
   }
 }
 
+TEST(HeapSnapshotScriptContext) {
+  LocalContext env;
+  v8::HandleScope scope(env->GetIsolate());
+  v8::HeapProfiler* heap_profiler = env->GetIsolate()->GetHeapProfiler();
+
+  CompileRun("class Foo{}; const foo = new Foo();");
+  const v8::HeapSnapshot* snapshot = heap_profiler->TakeHeapSnapshot();
+  CHECK(ValidateSnapshot(snapshot));
+  const v8::HeapGraphNode* global = GetGlobalObject(snapshot);
+  const v8::HeapGraphNode* native_context =
+      GetProperty(env->GetIsolate(), global, v8::HeapGraphEdge::kInternal,
+                  "native_context");
+  CHECK(native_context);
+  const v8::HeapGraphNode* script_context_table =
+      GetProperty(env->GetIsolate(), native_context,
+                  v8::HeapGraphEdge::kInternal, "script_context_table");
+  CHECK(script_context_table);
+  bool found_foo = false;
+  for (int i = 0, count = script_context_table->GetChildrenCount(); i < count;
+       ++i) {
+    const v8::HeapGraphNode* context =
+        script_context_table->GetChild(i)->GetToNode();
+    const v8::HeapGraphNode* foo = GetProperty(
+        env->GetIsolate(), context, v8::HeapGraphEdge::kContextVariable, "foo");
+    if (foo) {
+      found_foo = true;
+    }
+  }
+  CHECK(found_foo);
+}
+
 class EmbedderNode : public v8::EmbedderGraph::Node {
  public:
   EmbedderNode(const char* name, size_t size,