Use TaskScheduler instead of WorkerPool in v8_platform.cc.

extensions/renderer/module_system_test.h

Index: extensions/renderer/module_system_test.h
diff --git a/extensions/renderer/module_system_test.h b/extensions/renderer/module_system_test.h
index 1cfbb7c46fc116eb82db1d8e4f444edd315d6858..3508574dd8fb02756055630dbe7eba4c27b894a1 100644
--- a/extensions/renderer/module_system_test.h
+++ b/extensions/renderer/module_system_test.h
@@ -6,6 +6,7 @@
 #define EXTENSIONS_RENDERER_MODULE_SYSTEM_TEST_H_
 
 #include "base/macros.h"
+#include "base/test/scoped_async_task_scheduler.h"
 #include "extensions/renderer/module_system.h"
 #include "extensions/renderer/script_context.h"
 #include "gin/public/context_holder.h"
@@ -98,6 +99,10 @@ class ModuleSystemTest : public testing::Test {
   void RunResolvedPromises();
 
  private:
+  // Required by gin::V8Platform::CallOnBackgroundThread(). Can't be a
+  // ScopedTaskScheduler because v8 synchronously waits for tasks to run.
+  base::test::ScopedAsyncTaskScheduler scoped_async_task_scheduler_;
+
   v8::Isolate* isolate_;
   std::unique_ptr<ModuleSystemTestEnvironment> env_;
   bool should_assertions_be_made_;