[DevTools] Do not pause worklets on start

Worklets running in a separate thread do not have parent_devtools_token,
and so we don't support debugging them. This should probably be fixed.

Meanwhile, we should not also pause them on start - otherwise there is
no way to unpause because nobody is actually debugging them.

Bug: 901112
Change-Id: I63b59da95a1181ff03886f8fc233aa621726f1f8
Reviewed-on: https://chromium-review.googlesource.com/c/1313837Reviewed-by: Yi Gu <yigu@chromium.org>
Reviewed-by: Andrey Kosyakov <caseq@chromium.org>
Commit-Queue: Dmitry Gozman <dgozman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#605434}

third_party/blink/renderer/core/inspector/worker_inspector_controller.cc

@@ -84,6 +84,7 @@ WorkerInspectorController::WorkerInspectorController(
       Platform::Current()->GetIOTaskRunner();
   if (!parent_devtools_token_.is_empty() && io_task_runner) {
     // There may be no io task runner in unit tests.
+    wait_for_debugger_ = devtools_params->wait_for_debugger;
     agent_ = new DevToolsAgent(this, inspected_frames_.Get(), probe_sink_.Get(),
                                std::move(inspector_task_runner),
                                std::move(io_task_runner));
@@ -146,6 +147,13 @@ void WorkerInspectorController::FlushProtocolNotifications() {
     agent_->FlushProtocolNotifications();
 }
 
+void WorkerInspectorController::WaitForDebuggerIfNeeded() {
+  if (!wait_for_debugger_)
+    return;
+  wait_for_debugger_ = false;
+  debugger_->PauseWorkerOnStart(thread_);
+}
+
 void WorkerInspectorController::WillProcessTask(
     const base::PendingTask& pending_task) {}
 

third_party/blink/renderer/core/inspector/worker_inspector_controller.h

@@ -69,6 +69,7 @@ class WorkerInspectorController final
   DevToolsAgent* GetDevToolsAgent() const { return agent_.Get(); }
   void Dispose();
   void FlushProtocolNotifications();
+  void WaitForDebuggerIfNeeded();
 
  private:
   WorkerInspectorController(WorkerThread*,
@@ -99,6 +100,7 @@ class WorkerInspectorController final
   Member<InspectedFrames> inspected_frames_;
   Member<CoreProbeSink> probe_sink_;
   int session_count_ = 0;
+  bool wait_for_debugger_ = false;
 
   // These fields are set up in the constructor and then read
   // on a random thread from EmitTraceEvent().

third_party/blink/renderer/core/workers/worker_thread.cc

@@ -435,7 +435,6 @@ void WorkerThread::InitializeOnWorkerThread(
     const base::Optional<WorkerBackingThreadStartupData>& thread_startup_data,
     std::unique_ptr<WorkerDevToolsParams> devtools_params) {
   DCHECK(IsCurrentThread());
-  bool wait_for_debugger = devtools_params->wait_for_debugger;
   {
     MutexLocker lock(mutex_);
     DCHECK_EQ(ThreadState::kNotStarted, thread_state_);
@@ -492,11 +491,7 @@ void WorkerThread::InitializeOnWorkerThread(
   // Otherwise, InspectorTaskRunner might interrupt isolate execution
   // from another thread and try to resume "pause on start" before
   // we even paused.
-  if (wait_for_debugger) {
-    WorkerThreadDebugger* debugger = WorkerThreadDebugger::From(GetIsolate());
-    if (debugger)
-      debugger->PauseWorkerOnStart(this);
-  }
+  worker_inspector_controller_->WaitForDebuggerIfNeeded();
 }
 
 void WorkerThread::EvaluateClassicScriptOnWorkerThread(