Add user actions to startup tracing categories

Startup teams have a bunch of user actions they are
interested in.

Change-Id: I47e80d0d767b852ee89e3ed2f6dfe201246e3909
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2325651
Commit-Queue: ssid <ssid@chromium.org>
Commit-Queue: Eric Seckler <eseckler@chromium.org>
Auto-Submit: ssid <ssid@chromium.org>
Reviewed-by: Eric Seckler <eseckler@chromium.org>
Cr-Commit-Position: refs/heads/master@{#792614}

components/tracing/common/trace_startup_config.cc

@@ -40,7 +40,8 @@ const base::FilePath::CharType kAndroidTraceConfigFile[] =
 const char kDefaultStartupCategories[] =
     "startup,browser,toplevel,toplevel.flow,ipc,EarlyJava,cc,Java,navigation,"
     "loading,gpu,disabled-by-default-cpu_profiler,download_service,"
-    "disabled-by-default-histogram_samples,-*";
+    "disabled-by-default-histogram_samples,"
+    "disabled-by-default-user_action_samples,-*";
 #else
 const char kDefaultStartupCategories[] =
     "benchmark,toplevel,startup,disabled-by-default-file,toplevel.flow,"