Break down end-to-end scroll update latency UMA metrics

cc/trees/layer_tree_host_impl.cc

Index: cc/trees/layer_tree_host_impl.cc
diff --git a/cc/trees/layer_tree_host_impl.cc b/cc/trees/layer_tree_host_impl.cc
index 95e1ab1866834c9582ad4f95a117bbdbc44f97f2..cb977d85ced57891870491767159ff6f2868e21d 100644
--- a/cc/trees/layer_tree_host_impl.cc
+++ b/cc/trees/layer_tree_host_impl.cc
@@ -1650,12 +1650,19 @@ bool LayerTreeHostImpl::SwapBuffers(const LayerTreeHostImpl::FrameData& frame) {
   }
   CompositorFrameMetadata metadata = MakeCompositorFrameMetadata();
   active_tree()->FinishSwapPromises(&metadata);
-  for (size_t i = 0; i < metadata.latency_info.size(); i++) {
+  for (auto& latency : metadata.latency_info) {
     TRACE_EVENT_FLOW_STEP0(
         "input,benchmark",
         "LatencyInfo.Flow",
-        TRACE_ID_DONT_MANGLE(metadata.latency_info[i].trace_id),
+        TRACE_ID_DONT_MANGLE(latency.trace_id),
         "SwapBuffers");
+    // Only add the latency component once for renderer swap, not the browser
+    // swap.
+    if (!latency.FindLatency(ui::INPUT_EVENT_LATENCY_RENDERER_SWAP_COMPONENT,
+                             0, nullptr)) {
+      latency.AddLatencyNumber(ui::INPUT_EVENT_LATENCY_RENDERER_SWAP_COMPONENT,
+                               0, 0);
+    }
   }
   renderer_->SwapBuffers(metadata);
   return true;