Use ScopedTaskEnvironment instead of MessageLoop in tests that use v8.

chrome/test/base/v8_unit_test.cc

Index: chrome/test/base/v8_unit_test.cc
diff --git a/chrome/test/base/v8_unit_test.cc b/chrome/test/base/v8_unit_test.cc
index 55aefc43e14c6794186703bf676ba862d6f4ed05..c35563719f15b71cd10050edbae7b5c0e7a2424a 100644
--- a/chrome/test/base/v8_unit_test.cc
+++ b/chrome/test/base/v8_unit_test.cc
@@ -7,7 +7,6 @@
 #include "base/files/file_util.h"
 #include "base/logging.h"
 #include "base/memory/ptr_util.h"
-#include "base/message_loop/message_loop.h"
 #include "base/path_service.h"
 #include "base/strings/string_piece.h"
 #include "base/strings/stringprintf.h"
@@ -202,8 +201,6 @@ void V8UnitTest::SetUp() {
               console->NewInstance(context).ToLocalChecked())
         .ToChecked();
   }
-
-  loop_ = base::MakeUnique<base::MessageLoop>();
 }
 
 void V8UnitTest::SetGlobalStringVar(const std::string& var_name,