Make idle tasks optional in the default platform.

test/unittests/libplatform/default-platform-unittest.cc

 // Copyright 2014 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/libplatform/default-platform.h"
 #include "testing/gmock/include/gmock/gmock.h"
 
 using testing::InSequence;
 using testing::StrictMock;
 
 namespace v8 {
 namespace platform {
 
 namespace {
 
 struct MockTask : public Task {
   virtual ~MockTask() { Die(); }
   MOCK_METHOD0(Run, void());
   MOCK_METHOD0(Die, void());
 };
 
 struct MockIdleTask : public IdleTask {
   virtual ~MockIdleTask() { Die(); }
   MOCK_METHOD1(Run, void(double deadline_in_seconds));
   MOCK_METHOD0(Die, void());
 };
 
 class DefaultPlatformWithMockTime : public DefaultPlatform {
  public:
-  DefaultPlatformWithMockTime() : time_(0) {}
+  DefaultPlatformWithMockTime()
+      : DefaultPlatform(IdleTaskSupport::kEnabled), time_(0) {}
   double MonotonicallyIncreasingTime() override { return time_; }
   void IncreaseTime(double seconds) { time_ += seconds; }
 
  private:
   double time_;
 };
 
 }  // namespace
 
 
@@ skipping 115 matching lines @@
   {
     DefaultPlatformWithMockTime platform;
     StrictMock<MockIdleTask>* task = new StrictMock<MockIdleTask>;
     platform.CallIdleOnForegroundThread(isolate, task);
     EXPECT_CALL(*task, Die());
   }
 }
 
 }  // namespace platform
 }  // namespace v8