Implement scroll handler latency tracking

cc/trees/layer_tree_host_unittest.cc

Index: cc/trees/layer_tree_host_unittest.cc
diff --git a/cc/trees/layer_tree_host_unittest.cc b/cc/trees/layer_tree_host_unittest.cc
index 6e44cb2659f1914383e1b67de28a38c1e2b98376..9492884e21b3ce310e16c8224ebf179de536bd9d 100644
--- a/cc/trees/layer_tree_host_unittest.cc
+++ b/cc/trees/layer_tree_host_unittest.cc
@@ -4445,6 +4445,8 @@ class TestSwapPromise : public SwapPromise {
     result_->reason = reason;
   }
 
+  virtual int64 TraceId() const OVERRIDE { return 0; }
+
  private:
   // Not owned.
   TestSwapPromiseResult* result_;
@@ -4621,8 +4623,7 @@ class SimpleSwapPromiseMonitor : public SwapPromiseMonitor {
                            int* set_needs_commit_count,
                            int* set_needs_redraw_count)
       : SwapPromiseMonitor(layer_tree_host, layer_tree_host_impl),
-        set_needs_commit_count_(set_needs_commit_count),
-        set_needs_redraw_count_(set_needs_redraw_count) {}
+        set_needs_commit_count_(set_needs_commit_count) {}
 
   virtual ~SimpleSwapPromiseMonitor() {}
 
@@ -4631,12 +4632,15 @@ class SimpleSwapPromiseMonitor : public SwapPromiseMonitor {
   }
 
   virtual void OnSetNeedsRedrawOnImpl() OVERRIDE {
-    (*set_needs_redraw_count_)++;
+    ADD_FAILURE() << "Should not get called on main thread.";
+  }
+
+  virtual void OnForwardScrollUpdateToMainThreadOnImpl() OVERRIDE {
+    ADD_FAILURE() << "Should not get called on main thread.";
   }
 
  private:
   int* set_needs_commit_count_;
-  int* set_needs_redraw_count_;
 };
 
 class LayerTreeHostTestSimpleSwapPromiseMonitor : public LayerTreeHostTest {