[inspector] Cache task template for async stack tagging API

This CL changes `scheduleTask` to use a cached ObjectTemplate to
create the JS task objects. Console creates the template lazily upon
first use.

A local micro benchmark that creates 100k task objects shows a
speedup of roughly 4x.

R=jarin@chromium.org

Bug: chromium:1334585
Change-Id: Ice037ad32836fe428b1bcbee15738cb17877a3dd
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3779496
Commit-Queue: Simon Zünd <szuend@chromium.org>
Reviewed-by: Jaroslav Sevcik <jarin@chromium.org>
Cr-Commit-Position: refs/heads/main@{#81906}

src/inspector/v8-console.cc

@@ -594,13 +594,9 @@ void V8Console::scheduleTask(const v8::FunctionCallbackInfo<v8::Value>& info) {
     return;
   }
 
-  v8::Local<v8::External> data = v8::External::New(isolate, this);
-  v8::Local<v8::ObjectTemplate> taskTemplate = v8::ObjectTemplate::New(isolate);
-  v8::Local<v8::FunctionTemplate> funcTemplate = v8::FunctionTemplate::New(
-      isolate, &V8Console::call<&V8Console::runTask>, data);
-  taskTemplate->Set(isolate, "run", funcTemplate);
-  v8::Local<v8::Object> task =
-      taskTemplate->NewInstance(isolate->GetCurrentContext()).ToLocalChecked();
+  v8::Local<v8::Object> task = taskTemplate()
+                                   ->NewInstance(isolate->GetCurrentContext())
+                                   .ToLocalChecked();
 
   auto taskInfo = std::make_unique<TaskInfo>(isolate, this, task);
   void* taskId = taskInfo->Id();
@@ -657,6 +653,22 @@ v8::Local<v8::Private> V8Console::taskInfoKey() {
   return m_taskInfoKey.Get(isolate);
 }
 
+v8::Local<v8::ObjectTemplate> V8Console::taskTemplate() {
+  v8::Isolate* isolate = m_inspector->isolate();
+  if (!m_taskTemplate.IsEmpty()) {
+    return m_taskTemplate.Get(isolate);
+  }
+
+  v8::Local<v8::External> data = v8::External::New(isolate, this);
+  v8::Local<v8::ObjectTemplate> taskTemplate = v8::ObjectTemplate::New(isolate);
+  v8::Local<v8::FunctionTemplate> funcTemplate = v8::FunctionTemplate::New(
+      isolate, &V8Console::call<&V8Console::runTask>, data);
+  taskTemplate->Set(isolate, "run", funcTemplate);
+
+  m_taskTemplate.Reset(isolate, taskTemplate);
+  return taskTemplate;
+}
+
 void V8Console::cancelConsoleTask(TaskInfo* taskInfo) {
   m_inspector->asyncTaskCanceled(taskInfo->Id());
   m_tasks.erase(taskInfo->Id());

src/inspector/v8-console.h

@@ -14,6 +14,7 @@
 #include "src/debug/interface-types.h"
 
 namespace v8 {
+class ObjectTemplate;
 class Set;
 }  // namespace v8
 
@@ -201,6 +202,11 @@ class V8Console : public v8::debug::ConsoleDelegate {
   // Chromium's context snapshot.
   v8::Local<v8::Private> taskInfoKey();
 
+  // Lazily creates m_taskTemplate and returns a local handle to it.
+  // Similarly to m_taskInfoKey, we can't create the template upfront as to not
+  // be part of Chromium's context snapshot.
+  v8::Local<v8::ObjectTemplate> taskTemplate();
+
   V8InspectorImpl* m_inspector;
 
   // A map of unique pointers used for the scheduling and joining async stacks.
@@ -218,6 +224,11 @@ class V8Console : public v8::debug::ConsoleDelegate {
   // We use a private symbol to stash the `TaskInfo` as an v8::External on the
   // JS task objects created by `console.scheduleTask`.
   v8::Global<v8::Private> m_taskInfoKey;
+
+  // We cache the task template for the async stack tagging API for faster
+  // instantiation. Use `taskTemplate()` to retrieve the lazily created
+  // template.
+  v8::Global<v8::ObjectTemplate> m_taskTemplate;
 };
 
 /**