Use ScopedTaskEnvironment instead of MessageLoop in tests that use v8.

gin/test/v8_test.h

Index: gin/test/v8_test.h
diff --git a/gin/test/v8_test.h b/gin/test/v8_test.h
index 635281b16f028603ec5918663d775f5e019f13d7..383cd134af6084b1f059137e12920cb80abf9987 100644
--- a/gin/test/v8_test.h
+++ b/gin/test/v8_test.h
@@ -9,7 +9,7 @@
 
 #include "base/compiler_specific.h"
 #include "base/macros.h"
-#include "base/message_loop/message_loop.h"
+#include "base/test/scoped_task_environment.h"
 #include "testing/gtest/include/gtest/gtest.h"
 #include "v8/include/v8.h"
 
@@ -28,7 +28,7 @@ class V8Test : public testing::Test {
   void TearDown() override;
 
  protected:
-  base::MessageLoop message_loop_;
+  base::test::ScopedTaskEnvironment scoped_task_environment_;
   std::unique_ptr<IsolateHolder> instance_;
   v8::Persistent<v8::Context> context_;