Make idle tasks optional in the default platform.

test/unittests/run-all-unittests.cc

Index: test/unittests/run-all-unittests.cc
diff --git a/test/unittests/run-all-unittests.cc b/test/unittests/run-all-unittests.cc
index 58cac6afa9087a570b5aa406c972b360e6c6e368..55217ae2bbdbb965a93dec6eaf98dad003c047ed 100644
--- a/test/unittests/run-all-unittests.cc
+++ b/test/unittests/run-all-unittests.cc
@@ -15,7 +15,8 @@ class DefaultPlatformEnvironment final : public ::testing::Environment {
 
   void SetUp() override {
     EXPECT_EQ(NULL, platform_);
-    platform_ = v8::platform::CreateDefaultPlatform();
+    platform_ = v8::platform::CreateDefaultPlatform(
+        0, v8::platform::IdleTaskSupport::kEnabled);
     ASSERT_TRUE(platform_ != NULL);
     v8::V8::InitializePlatform(platform_);
     ASSERT_TRUE(v8::V8::Initialize());