Remove WebScheduler::shutdown() which is no longer needed.

Source/platform/scheduler/SchedulerTest.cpp

Index: Source/platform/scheduler/SchedulerTest.cpp
diff --git a/Source/platform/scheduler/SchedulerTest.cpp b/Source/platform/scheduler/SchedulerTest.cpp
index 0f6679a84a8183607b59b5e7a08240cc6e646c55..e940f57ebcaa373a60f8432b0fb80a3ca624650c 100644
--- a/Source/platform/scheduler/SchedulerTest.cpp
+++ b/Source/platform/scheduler/SchedulerTest.cpp
@@ -34,16 +34,10 @@ class WebSchedulerForTest : public WebScheduler {
 public:
     WebSchedulerForTest()
         : m_shouldYieldForHighPriorityWork(false)
-        , m_didShutdown(false)
     {
     }
 
     // WebScheduler implementation:
-    void shutdown() override
-    {
-        m_didShutdown = true;
-    }
-
     bool shouldYieldForHighPriorityWork() override
     {
         return m_shouldYieldForHighPriorityWork;
@@ -54,11 +48,6 @@ public:
         m_latestIdleTask = adoptPtr(task);
     }
 
-    bool didShutdown() const
-    {
-        return m_didShutdown;
-    }
-
     void setShouldYieldForHighPriorityWork(bool shouldYieldForHighPriorityWork)
     {
         m_shouldYieldForHighPriorityWork = shouldYieldForHighPriorityWork;
@@ -72,7 +61,6 @@ public:
 
 protected:
     bool m_shouldYieldForHighPriorityWork;
-    bool m_didShutdown;
 
     OwnPtr<WebScheduler::IdleTask> m_latestIdleTask;
 };
@@ -91,13 +79,6 @@ protected:
     OwnPtr<SchedulerForTest> m_scheduler;
 };
 
-TEST_F(SchedulerTest, TestShutdown)
-{
-    EXPECT_FALSE(m_webScheduler->didShutdown());
-    m_scheduler.clear();
-    EXPECT_TRUE(m_webScheduler->didShutdown());
-}
-
 TEST_F(SchedulerTest, TestShouldYield)
 {
     EXPECT_FALSE(m_scheduler->shouldYieldForHighPriorityWork());