Implement compositor thread VSync aligned event queue

cc/trees/layer_tree_host_unittest_scroll.cc

Index: cc/trees/layer_tree_host_unittest_scroll.cc
diff --git a/cc/trees/layer_tree_host_unittest_scroll.cc b/cc/trees/layer_tree_host_unittest_scroll.cc
index 10e17abf33fa0b4e72680ee90dce9ec0e96e0b7f..bba785f75e7a9dd482bee357e5f44de7c3b73df5 100644
--- a/cc/trees/layer_tree_host_unittest_scroll.cc
+++ b/cc/trees/layer_tree_host_unittest_scroll.cc
@@ -1287,6 +1287,12 @@ class ThreadCheckingInputHandlerClient : public InputHandlerClient {
     }
   }
 
+  void DeliverInputForBeginFrame() override {
+    if (!task_runner_->BelongsToCurrentThread()) {
+      ADD_FAILURE() << "DeliverInputForBeginFrame called on wrong thread";
+    }
+  }
+
  private:
   base::SingleThreadTaskRunner* task_runner_;
   bool* received_stop_flinging_;
@@ -1815,6 +1821,7 @@ class MockInputHandlerClient : public InputHandlerClient {
       float page_scale_factor,
       float min_page_scale_factor,
       float max_page_scale_factor) override {}
+  void DeliverInputForBeginFrame() override {}
 };
 
 // This is a regression test, see crbug.com/639046.