Schedule bitmap animation timers on the compositor task runner.

third_party/WebKit/Source/core/dom/IdleDeadlineTest.cpp

Index: third_party/WebKit/Source/core/dom/IdleDeadlineTest.cpp
diff --git a/third_party/WebKit/Source/core/dom/IdleDeadlineTest.cpp b/third_party/WebKit/Source/core/dom/IdleDeadlineTest.cpp
index d68f3ff8cf8551d2e6b7aad5be9ea0ac3e0ab7f2..cf737eadc61dbcad6e97383e60364c86510f171d 100644
--- a/third_party/WebKit/Source/core/dom/IdleDeadlineTest.cpp
+++ b/third_party/WebKit/Source/core/dom/IdleDeadlineTest.cpp
@@ -31,6 +31,7 @@ class MockScheduler final : public WebScheduler {
       WebViewScheduler::WebViewSchedulerSettings*) override {
     return nullptr;
   }
+  WebTaskRunner* CompositorTaskRunner() override { return nullptr; }
   void SuspendTimerQueue() override {}
   void ResumeTimerQueue() override {}
   void AddPendingNavigation(