Update mojo_benchmark documentation.

R=qsr@chromium.org

Review URL: https://codereview.chromium.org/1351523004 .

mojo/devtools/common/docs/mojo_benchmark.md

diff --git a/mojo/devtools/common/docs/mojo_benchmark.md b/mojo/devtools/common/docs/mojo_benchmark.md
index 6e274d7..17bc76e 100644
--- a/mojo/devtools/common/docs/mojo_benchmark.md
+++ b/mojo/devtools/common/docs/mojo_benchmark.md
@@ -38,10 +38,11 @@
 
 ## Caching
 
-The script runs each benchmark twice. The first run (**cold start**) clears the
-following caches before start:
+The script runs each benchmark twice. The first run (**cold start**) clears
+caches of the following apps on startup:
 
- - url_response_disk_cache
+ - network_service.mojo
+ - url_response_disk_cache.mojo
 
 The second run (**warm start**) runs immediately afterwards, without clearing
 any caches.