Add basic tracing support to the gtest launcher

base/test/test_switches.cc

Index: base/test/test_switches.cc
diff --git a/base/test/test_switches.cc b/base/test/test_switches.cc
index 40f20d7b7dbebdfa66fa9acc9aee4fba1578ab23..817a38edb18f56bf5c1f9354977b7497fdd8ce44 100644
--- a/base/test/test_switches.cc
+++ b/base/test/test_switches.cc
@@ -62,6 +62,10 @@ const char switches::kTestLauncherTotalShards[] =
 
 // Time (in milliseconds) that the tests should wait before timing out.
 const char switches::kTestLauncherTimeout[] = "test-launcher-timeout";
+
+// Path where to save a trace of test launcher's execution.
+const char switches::kTestLauncherTrace[] = "test-launcher-trace";
+
 // TODO(phajdan.jr): Clean up the switch names.
 const char switches::kTestTinyTimeout[] = "test-tiny-timeout";
 const char switches::kUiTestActionTimeout[] = "ui-test-action-timeout";