[cc/metrics] Enable a new trace-event for benchmarks.

Allow the LayerTreeHostImpl::SetVisible trace-event to be collected in
traces, so that we can measure how long a page is visible for.

BUG=1125152

Change-Id: I1be619aca28c88f834bbde989872be68e9f94e38
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2422144
Auto-Submit: Sadrul Chowdhury <sadrul@chromium.org>
Commit-Queue: Behdad Bakhshinategh <behdadb@chromium.org>
Reviewed-by: Behdad Bakhshinategh <behdadb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#808958}

cc/trees/layer_tree_host_impl.cc

@@ -192,14 +192,14 @@ viz::ResourceFormat TileRasterBufferFormat(
 
 void DidVisibilityChange(LayerTreeHostImpl* id, bool visible) {
   if (visible) {
-    TRACE_EVENT_NESTABLE_ASYNC_BEGIN1("cc", "LayerTreeHostImpl::SetVisible",
-                                      TRACE_ID_LOCAL(id), "LayerTreeHostImpl",
-                                      id);
+    TRACE_EVENT_NESTABLE_ASYNC_BEGIN1(
+        "cc,benchmark", "LayerTreeHostImpl::SetVisible", TRACE_ID_LOCAL(id),
+        "LayerTreeHostImpl", id);
     return;
   }
 
-  TRACE_EVENT_NESTABLE_ASYNC_END0("cc", "LayerTreeHostImpl::SetVisible",
-                                  TRACE_ID_LOCAL(id));
+  TRACE_EVENT_NESTABLE_ASYNC_END0(
+      "cc,benchmark", "LayerTreeHostImpl::SetVisible", TRACE_ID_LOCAL(id));
 }
 
 void PopulateMetadataContentColorUsage(