Make EventHandler::ActiveIntervalTimer mockable.

Source/platform/Timer.h

Index: Source/platform/Timer.h
diff --git a/Source/platform/Timer.h b/Source/platform/Timer.h
index 4bf89004d96fcfb407e6166329c946d56dac99f5..589708a6ad5dbecfce4a5bd27d821ba55d783f74 100644
--- a/Source/platform/Timer.h
+++ b/Source/platform/Timer.h
@@ -105,8 +105,12 @@ private:
     friend class TimerHeapReference;
 };
 
+template <typename TimerFiredClass> class MockableTimer;
+
 template <typename TimerFiredClass>
-class Timer FINAL : public TimerBase {
+class Timer : public TimerBase {
+    friend class MockableTimer<TimerFiredClass>;
+
 public:
     typedef void (TimerFiredClass::*TimerFiredFunction)(Timer*);
 
@@ -120,6 +124,46 @@ private:
     TimerFiredFunction m_function;
 };
 
+// A mockable timer is useful in manually controlling timers from tests
+// to avoid flakiness. To access a specific instance in layout tests,
+// it has to be plumbed through internals.
+template <typename TimerFiredClass>
+class MockableTimer FINAL : public Timer<TimerFiredClass> {
+public:
+    typedef typename Timer<TimerFiredClass>::TimerFiredFunction TimerFiredFunction;
+
+    MockableTimer(TimerFiredClass* o, TimerFiredFunction f)
+        : Timer<TimerFiredClass>(o, f)
+        , m_manualMode(false)
+        , m_firePending(false)
+    {
+    }
+
+    void setManualModeForTesting(bool manualMode) { m_manualMode = manualMode; }
+
+    void manualFireForTesting()
+    {
+        ASSERT(m_manualMode);
+        ASSERT(Timer<TimerFiredClass>::isActive() || m_firePending);
+        Timer<TimerFiredClass>::fired();
+        if (!Timer<TimerFiredClass>::repeatInterval())
+            Timer<TimerFiredClass>::stop();
+        m_firePending = false;
+    }
+
+private:
+    bool m_manualMode;
+    bool m_firePending;
+
+    virtual void fired() OVERRIDE
+    {
+        if (m_manualMode)
+            m_firePending = true;
+        else
+            Timer<TimerFiredClass>::fired();
+    }
+};
+
 inline bool TimerBase::isActive() const
 {
     ASSERT(m_thread == currentThread());